Jill, maybe she's not as bad as the people on TV, but I bet there are some psychological issues behind this. What you described is what my grandfather's house (well, shack, to be honest) looked like on the one time I remember visiting. You literally could hardly move. It was very much his personality. He had a lot of issues. I'm not saying your mother does, but I'd tread carefully. If you have a good enough relationship with your mother, you could ask her why she's holding on to all that stuff. Find out if she can identify any possible benefit to getting rid of some of it. I think just sneaking in and cleaning the place out without her permission might cause a major ruckus. Not only might it poison your relationship with her, but I bet she'd just starting hoarding right away again anyway.

If the house is livable (fairly clean and room to move around), then to be honest, the hoarded stuff isn't doing any harm. Sure it looks ugly and it's annoying, but unless there are health or safety concerns it may have to be a case of live and let live.

Thank you everyone for your ideas and support on this. We have been working on the issue and having improved some. Slightly, but certainly a step forward. I was able to get her to get rid of 10 garbage bags full of clothes and linen, yes, 10 just out of her closet. So now my dad was able to move his clothes that have been in the spare bedroom closet, back to his own bedroom with her. It's been SOOOO long since they have been able to share a closet. She went into panic at first, thinking OMG I have nothing to wear. But I reminded her in actuality, she has MORE to wear than before, because she can access it all.

That is AWESOME!!! And good for you for being her cheerleader. I find a big part of my keeping stuff is the thought process. If you remind her of the benefits, then she can start learning to remind herself of the benefits, and then it becomes easier to maintain. Slow and steady.