Can my sister in law stop me from putting my mom in assisted living?

My sibs decided they wanted to move mom. I got tired of the dysfunction and after four years of 24/7 care for mom nad her hubby and gave in. The decline in mom with dementia was drastic. He also declined, and passed a few days ago. Mom was accepted for hospice about the same time. Be very careful and do not make this decision to ease your feelings of guilt for not being able or wanting to help. What will result if that is the reason is nothing short of very heartbreaking to watch!

What makes you think mom is not getting proper care where she is? Who has POA? Is mom competent? If so, she gets to choose where she lives. If not, then she needs to be found incompetent to force the issue.

It's not up to either of you, it is up to mom. If your mother says she is not getting enough attention, beware, she may just be fibbing to get your attention and make you feel sorry for her. Very common.
Placing a parent without their consent requires a court order and judges will sympathize with the wishes of the parent.

Who has POA? And what does you mom want?