Needing some advice on my step daughter’s situation

Natasha

So my step daughter as of recently has been living with us full time. Her mom used to take her almost every Saturday to Sunday but has stopped seeing her all together. It’s been almost 2 months since she has seen her mom. It has been causing some issues at home with how she treats me but I expect that since I’m the closet thing to a mom for her but just recently, she has started to hit herself with her toys after she gets put in a time out for something. She did it today after being put in a time out and she left a really big mark on her leg. Has any other step mom’s ever have this happen and if so. What did you to do help the child? Thanks in advance!