It is so tough to be the mother of an addict. It is almost hardwired in us that our job as a parent is to "save" them. We may accept in our heads that we didn't cause it, can't control it, and can't cure it...but it takes longer to sink in to our hearts.
It really is up to her, though. She is 24 years old- and yes, she has damaged her brain with drugs...that's absolutely true. But...she is an adult, and entitled to the dignity of making her own mistakes.
The same is true of your mother - while I think it's a horrible idea for your mother to take her in...she needs to make that decision herself.
There is no right thing to do to "fix" your daughter. If there was, we wouldn't be here on SR. ALL our lived ones would be fixed. There are only things you can do to find peace for yourselves.
You need to decide what you need to do for yourself to find peace. If you are not ready to let go of trying to figure out how to save your daughter entirely...set some limits. Allow yourself an hour a day to research programs/solutions/whatever...and then try to focus on doing things for yourself. AlAnon meetings, getting together with friends, reading a non-addiction-related book, going for a walk- whatever...spend some time on rebuilding your own life.