Help! I live with a hoarder!

I got divorced a year ago and my 3 kids (12,12,8) moved in with my mom. She’s lived alone in this huge house for 20 years and I don’t think she’s ever thrown anything out. I’m trying hard to declutter my stuff and the kids stuff- which is very difficult for me- but she won’t let me throw out things. When I have the energy I am able to get rid of a few things here and there but it’s never enough. She’s 73 and not gonna change her ways anytime soon. Any advice?