Step daughter acting inappropriate

I really just need to vent here. 
So I have a 9 year old boy from a previous relationship and my husband has a 6 year old girl. 
And we have recently just had our own baby. 
This year she started school and they go to school together. 
Since she started going to school she spends the week with us. 
So ever since then she has started having really inappropriate behaviors (I don't know if she was like this in her daycare days). 
She likes hugging and kissing children at school and she does the same to my kid who hates it and ends up locking himself in his room to avoid her. 
She chases him all day to the point she tells kids at her class he's her boyfriend. 
 Another day standing in line for ice cream after picking them up from school she rubbed her but on a boys crouch (she's only 6). 
I was so embarrassed I Immediately left with them. 
I did talk to her mom about it and I talked to her she says she's sorry and puts her baby face on and her thumb in her mouth (which I find disgusting but her mom thinks it's cute). 
I'm not mean to her at all, matter of fact she loves me. 
So during the summer vacation she is in a daycare cause my husband had to leave for 6 weeks (army) and it would be too much for me alone with a 3 months old baby and my kid. 
During this time her mom had to travel for work for 3 days (Friday till Sunday) and I've stayed with her being that she has aunts and 2 grandmothers and I only have my mother in law being that I have no other family in the US. 
Now I don't mind having her over at all she has siblings here. 
So this weekend her mother had to travel again and I'm staying with her despite my mother in law saying I shouldn't (they don't get along so well). 
So today I go down stairs to let the dog out and come back to my kid screaming at her telling her to stop and locking himself up in the baby room because she was chasing him pulling her pants down trying to expose herself to him. 
So I talked to her again telling her that behavior is not appropriate so she apologized and stopped. 
Later on while they were playing video game again my kid is screaming stop cause she was trying to sit on his neck while he was sitting on the floor. 
So I immediately called her mom cause I had enough and talking apparently doesn't work. So I have her mom on speaker and tell her the whole story she talked to her and her mom asked her what happened and she told her the whole story (good cause it didn't sound like I was making it up). 
So her mom has a little talk to her asking her if she's having fun and so on and tells her to apologize. 
Then turns back to me and says she's probably "cranky" (she's 6) cause it's past her bedtime. And tells me she should be in bed by 8 (it was past 9 when I called her). 
I forgot to mention she also put a pillow on top of my baby when she was on her swing chair. 
So I hate to be the "bitch" stepmom her but I really don't want her around anymore. And I hate it cause I want our family to get along but I can't have her around if this behavior doesn't stop. 
Sorry about the long text I just really needed to vent.