Одинокая мать и племянница

I need to get this off my chest so maybe I can stop crying...

My niece is turning 16.. she's lived with me for past 5 mo.. due to her mom being a active drug addict/ acholic and her dad (my bro has been in prison for 7 years comes home aug).. in the past 2 yrs my niece has endured alot of abuse (physical, sexual, emotional).. her mom knew she was goin to lose her kids if she didn't place them somewhere, she picked up 3 charges.. I've always been close to my niece so we was excited when she asked me to take her in.. I'm a single mom of a teen boy & 2 dogs.. I have paid for 1 call weekly and 1 visit a mo since day 1 my bro went down (only drug charges- no violent nor child related).. Ive giving her mom lots of money over the past 7 yrs for caring for my niece.. when she came to live with me we agreed she give me guardianship and $100 a mo.. when she went in to do time I would pay for 1 call a week.. her charges are 1 child endangerment (younger sis) drunk driving and position cs she also got a child endangerment back in 2019..

Found out she turns her self in 1st of May.. she has not paid me a dime.. she called my niece a week ago and asked what we was doin for bday? My niece told her that money is extremely tight due to me purchasing her cloths and etc.. her mom blew up and threatened to come get her since I can't afford to celebrate her 16th bday.. (legally she can't).. 2 days later she called apologized and told her she would send her $75 to do whatever she wanted.. my niece got excited and picked out pair shoes sent her a pic... She has called and txted her several times with no reply.. my niece has cried yest n today cause she said she knew not to believe her mom.. it broke my heart.. she already has bad anxiety and depression, her peers bully her due to her lazy eye... She's been thru so much...I can't do anything at moment cause I had to get her settled in no able to work as much..

I just don't feel as I should pay for calls since she didn't hold up her end plus for what she did bout her bday..