Your sister is mentally ill. Hoarding is a mental disorder. They are compelled to keep stuff--even stuff you or I would think of as trash--because each thing they have has some type of "emotion" attached to it. Or it's something they've "saved" from the garbage heap and it's not that bad and someone can use it (even if it's in such bad condition that no one would want it even if it were given away for free).
I never realized that people were actually this way until I watched the show HOARDERS on TV. My husband can't stand to watch that show, because he can't stand to see people living that way.
Yes, it's very sad. Yes, we want to help them. However, in your sister's case, she's been doing this for a very long time. She has rooms stacked full; the basement's full. She can't even come and clean out/move her stuff (usually because a hoarder cannot figure out what should stay/what should get tossed. In their mind, nothing should be gotten rid of. They physically become ill when they have to make the decision of keep, throw, or donate).
I agree with another poster; what you took out of the house to sell to consignment, what's left over, DO NOT give back to your sister. She'll just throw it on her pile of junk, and the junk pile will just keep growing. Tell her you don't have it anymore (throw it, donate, recycle it, just get rid of whatever you still have that came from your sister's place). As one poster said, I'm not sure I would have even told her that you had taken anything. She has so much junk that I seriously don't think she would have ever noticed that this or that is missing. However, now that you've brought it to her attention, she is probably having an OCD moment (obsessive-compulsive).
If she continues to get verbally abusive and/or starts to try to physically harm you, then you have no choice but to get a restraining order and/or call in professionals to help your sister. In fact, she needs help regardless. Cats peeing on everything not only stinks, but she might have rodents and insects and other critters living in all the stuff that makes the living condition unsafe/unsanitory.
If you have NetFlix, see if you can find some of the TV shows on hoarding and watch them. It really is eye opening to see how people with this disease think. Some of them are quite professional people. You'd never think that they would live the way they do.