How do we prove BM is an unfit parent?

So far she has under dressed the child (1 year old)on too many occations to count. We found from an old neighbor that on Halloween BM has baby in costume only (pumpkin) no socks, no pants, no shoes, nothing on his head, etc and it was less than 60 degrees and windy that evening. BM dropped him off at the grandparents with pants on plus his costume plus a soaking wet through the pants diaper. Bm will dress him in just a onsie when it like 55 degrees outside and when questioned she will say stuff like he gets hot. I have yet to see him come to us with socks on - no matter the weather he is not wearing them. Yes, he likes to take them off but if you buy the longer ones he can't get them off or put slippers on his feet. Never seen him in a hat except to show dad how cute it looks. She did give us sunglasses for him to wear once but that did not last either. He never wore a snowsuit or hat last winter when he was a newborn. BM would stuff blankets around him in the carseat and said that was good enough. What is they got stranded or had an accident? The baby could have frozen to death.

He comes to us dirty, I mean smelly (think smelly dude armpit)with nasty hair, dirty finger and toe nails (how does a child who cannot crawl get dirty nails?) and filthy ears everytime we get him. He has to be bathed almost as soon as we get him to the house. His diaper has to be changed before we can leave the exchange place or he would be soaked to the skin before we got home.

I have observed BM lifting the child up in the carseat, at an angle, without buckling him in first. I have also sen her toss him in the air as a newborn.

BM has made nasty comments to neighbors about behavior that baby has done such as if he cried like that for me or did this or that to me I would smack him.

HELP, HELP what can we do or find out to prove she is unfit. She does take meds for depression and has a family history of physical and sexual abuse.

Any advise would be wonderful.