What should I do or what can I do about my 28 year old sister?

Well it is a problem for me that my 28 year old sister is staying at my moms house and giving my mom sooooo many problems. my sister is on welfare has a two year old daughter and wont leave my moms house she is an ex drug user, she is addicted to her cell phone and on top of this she does not give my mom any money for anything she also gets food stamps and all she buys is junk food and foods like microwavable and cup noodle soups ect. and all these foods are bad for my mom because she is type 2 diabetic cholesterol high blood pressure and heart problems, my mom cant work she is in disability she got injured at work badly so she cant work any more, so when my mom gets her money she buys what she needs for the whole month you know fruits veggies fish chicken as healthy as she can. but the thing is that my sister cooks and makes unhealthy food and finishes my moms groceries, every sunday i take my mom water bottles and food for a whole week i also take her stuff to make her a healthy breakfast. every time i go there she is sittin in the sofa eating and talking on the phone and her daughter there untaken care off lets her do what she wants, another thing is that she has my moms house dirty she wont clean up after herself at all my mom has to tell her to do the dishes and she gets mad because of it, my mom already told her to leave plenty of times but my sister wont go, because she says she has no where to go, she has rented rooms before but noone can stand her being dirty and yelling and bad mouth and being lazy. there are alot of people that rent rooms for 400 dollars she can afford on top of every thing my mom is on a program that helps her pay for her rent and she might loose her apartment, another thing the apartment were my mom used to live she got kicked out because of my sister she was not in the contract so they found out and kicked out my mom. and on this appartment she already got a 2nd notice 3rd notice and shes out, my sister smokes too neighbors complaind and my mom got the 1st notice 2nd notice was too much noise (yelling and baby crying). the only kind of good thing my sister did was to stop smoking, my mom was sooooooo stressed the other day she had an asthma attack I had to take her to the hospital and she stayed there for 2 days dr said she had to take it easy but who can with a daughter like that. ive talked to my mom and told her to tell her to leave but she wont, i dont get it she says where she gonna go with her daughter I said she can afford a room like before she can go to a shelter no family member will take her because of how she is and she is tough she says she doesnt care and no one is going to change her that how she is. Oh and that baby has a dad but hes a looser and he s in jail. she says that when he comes out hes gonna get her and the baby a house and all these things i seriously doubt it. because when he was with her before he got in jail they were living on the streets and using drugs both of them. and then he got in jail 2 years ago. so since my mom wont accept a penny from her she spends it on who knows what because she dosent buy clothes for her or the baby the only thing she buys for the baby is diapers that is it the rest she pays for her stupid cell phone and the rest who knows. I already confronted my sister but she doesnt care as long as my mom wont teller to leave again she ignores my mom even if my mom tells her to go. So what should I do?