I would really encourage you to read the book "Stepmonster" by Wednesday Martin. Really, it is down to the behaviour of the girl's bio parents, as to whether you and she are able to form any sort of relationship - and this book explains why. There is really nothing much you can do to make it better.

As you say, the age thing probably isn't helping either. Don't make a huge effort, which will be wasted, but do be polite and civil. If she's 16, you don't have THAT many years ahead in which you will have to deal with her visitations.

Its possible she is not comfortable around you yet and is telling her dad what he wants to hear. But it's also possible that she does like you but lacks the social skills to be friendly and chatty with you in the way you would like. Children that age often have little idea what to talk to an older person about, so although she may be relaxed around her Dad or friends her own age, she might be struggling to talk to you. I imagine you're also at a bit of a loss about what to talk to her about. The awkward silence when you are left alone is probably entirely mutual, and no more an indicator that she doesn't like you than it is an indicator that you don't like her.

With all of my teen SD's I generally had to make most of the running in the conversation department and familiarise myself with the things that interested them. Here are some things you could try to establish some common ground with her:
1. Note what programmes she likes and start following one or more of them. If possible find one you can watch together when she's visiting, then you can discuss plots and characters
2. Buy gossip/celebrity magazines to have in the living room. Teens generally eat these up and will happily sit around the living room reading and remarking on some of the stories. It will clue you in on people and issues she is interested in and provide topics for conversation 'did you see x has done this' etc etc
3.Show an interest in her life, ask about her friends, give her openings to share things she and her friends have been up to and follow up on things she has mentioned before 'so how was the sleepover with x'
4.Avoid asking about school, other than with reference to friends and activities, it mostly makes teens switch off
5. Try to come up with some new traditions/routines based around simple distractions: movie night with popcorn etc
6. Use music to ease the mood. I had music tastes in common with my SD's and having music playing that we all liked made everyone more relaxed and upbeat. To this day I will often put music on before they get here when they are visiting as it relaxes me and makes things more upbeat and sociable

So, assume she likes you, capitalise on the fact that you are only 23 and probably have tastes in common, and give it a few months. Remember your goal is to have a pleasant relationship so you feel relaxed around each other, not to be her best friend or have the closeness of a parent. Try not to agonise about making her like you. Make a reasonable effort to put her at her ease and foster a pleasant relationship. If she doesn't respond, then take your lead from that and let it lie.

I want to say one other thing, given the age difference you should really be considering much bigger issues than whether his daughter likes you. You're investing in a relationship with someone who is in a very different place in terms of life experience and parenting. You seem torn between concern about your relationship with his daughter, and insecurity about your relative importance to your boyfriend.

Even if you establish a good relationship with his daughter and she made the effort you wish for, it is unlikely to put to rest your concerns about coming first in your boyfriends attentions. You're very young to settle for a relationship in which there will be a measure of competition for time and attention because he has this very important commitment to his relationship with his daughter. Many of us entered these situations older and, in some cases, wiser, and still struggled with those emotions.

You may imagine that if she warmed to you, you would feel better about things and 'part of the family', but it is nigh on impossible to create that sense of an inclusive family when the stepchild is already 16 when you start out. You can find common ground and things you can both talk about, but in all likelihood there will always be a measure of resentment and extra effort on your part. In 2 years she will be an adult and may then have less of a role in your life, and that may be the saving grace, but then there is the issue of your own future in terms of marriage and having children. Your BF had a long term GF after divorce but never married her. Is he anti-marriage? Do you want to get married some day? At 23 you may not yet know whether you yourself want children, but it is important to know whether your 46 year old boyfriend would even be open to that idea, or you are closing off all sorts of avenues which could provide further scope for resentment.

dw1989, The daughter isn't the problem. If I were 16 and my 40-something dad started dating a 23 year old, I would find that extremely awkward. And if I were a shy teenage girl, I probably wouldn't know what to say to you.

I think you're right to let them have alone time together. What is a shame is your BF forcing his daughter on you. I hate it when I read about bio parents forcing their significant other's to bond with their kids. Your BF needs to back off and let you do your own thing, and he and his daughter can do his own thing.

Also, I don't really understand why you want to settle for this situation which you yourself say is really awkward. You are so young and can easily find a young man without kids, or even a man in his 30's without kids. Don't let your BF dictate to you what your role is in his life and his daughter's life. The relationship between you and the daughter is between you and the daughter, not your BF, as long as you're not being cruel or abusive to her, he needs to back off! And you are an adult, you can refuse to go with your BF and his daughter if you want. He's not your dad, after all. See where I'm going with this? You're not his employee and you're not his child, so your BF can't boss you around, unless you let him.

And when you and his daughter are alone together and it gets awkward, just make some small talk, how was your day, what did you do, and if she's non-responsive, turn on the tv, read a magazine or do what everyone else does and glue your eyes to your smart phone.

I agree your bf needs to back off and allow you to not be part of everything he does with his daughter. She will probably appreciate as well that you are not hogging all of her dad's time when it's her time with him. You have your alone time with him.

Take it very slow with her to start. Allow her lots of time with her dad. Slowly build in some time with the three of you and show her during those times how interested you are in her, her opinions....lots of opportunities to ask her what she thinks about this or that on the news, how her sleepover with friend went., etc... Try to build in a little alone time where there are shared interests between you and her a hobby you enjoy or movie you both want to see

Don't worry about her liking you right now. Just focus on slowly building a relationship with her, slow being the key word. Allow her time to become comfortable with it. Don't expect a lot of the relationship and if she chooses not to have one with you, then respect her decision.

If she chooses to have a relationship with you however minor, even one based on mere tolerance for her dad's sake then be grateful you have that and turn her time alone with dad into something fun and separate for yourself - see friends or family, do something fun, enjoy your time off from the situation