grand daughter rights to stay wih grand mother in her house?

Depends on who has the legal right to make your mother's decisions for her. If your Mother retains that right.... no one else has it. If your sister managed to obtain that right (it's a legal issue), then she has it. Have you kept track of what's going on? Do you have any idea what is your Mother's intent? Find out if your sister has wrangled legal Power of Attorney over your Mother. That's not the same as POA at the bank to do her banking. For her to obtain POA over your Mother and her estate.... that takes legal papers and formal declaration. Find out. 

Unless your step sister owns the home or is your mother's guardian, she can't have your daughter forceably removed. The police won't do anything. Depending on your local laws, your daughter may have tenant's rights and need to be formally evicted. Your mother can kick her out though, even if she is being pressured in to it. Your mother and daughter need to make a formal rental agreement. This will protect both of them and make the terms of their arrangement clear. Your mother also needs to get her affairs in order and name a guardian in the event that she can't make decisions for herself. It is very possible that your step sister could claim that role if your mother does not make her wishes known.

i wouldnt stay somewhere if they told me to move out