It's good that you are reaching out for help for your sister.
You said, "She was diagnosed with bipolar disease over 10 years ago" and that "She has cluttered about 80 percent of our home. She claims that she is selling stuff in flea markets."
Has she ever seen a doctor for her bipolar? Has she ever taken any meds for that?
Is depressed or manic? Being treated for the bipolar may help her with the hoarding.
I looked on the net search engine by typing in "hoarders" and it had a number of websites.
One of them was titled, "Anxiety and Depression Association of America (aada.org). You could get the names of therapists who worked with people like that.
When I click on "hoarders" in the website, nothing happened, but what was occurring was the new data that came up didn't appear on the screen where I clicked on that, it appeared below it, by scrolling down.
With a website title like "Anxiety and Depression," sounds like there might be a lot of anxiety and depression associated with that ailment. I think some depression meds also help with anxiety, and if she is bipolar, they can give her something for the mania.
The key is getting her some help, in my view. Have you tried getting your sister to a psychiatrist? Sounds like she is in dire need of assistance, which you giving her.
Keep trying to help her. How about letting us know what is going on.