Hello Dragonfly. One of the more common ways to treat hoarding is Cognitive Behavioural Therapy (CBT). Unfortunately that only works if the hoarder admits that they have a problem. Other than that I don't know a lot about cures. I do know a little about hoarding. Like all of my writing, it may or may not be helpful, but if you read it with a bit of a smile on your face, you may find a little humour in it. I have included a website that does address some ways to discuss hoarding with a loved one.
Hoarding can involve a lot of different items or just some specific items. For example I don't know how many women that I have known that have a zillion recipes filed away that they will never use or boxes of yarn that will never be knitted. ( for guys I could include hoarded items like old magazines, articles on repairing items and socks with a hole in them LOL) None of these people would be considered hoarders, but of course they are (or I am) .
So sometimes it is not the fact that a person is a hoarder but it's the depth of their hoarding that comes to people's attention. Space also is a factor. An old friend of mine was never consider a hoarder. His home was always neat and tidy with no clutter. When he passed on, his family discovered that in his bush he had built 6 rough barn like structures that were absolutely filled with junk. It took them weeks to take everything to the dump. While he was alive nobody considered him a hoarder, because he had the space and kept it out of sight. But yrs of accumulated old tractors, car parts, clothing and other junk said otherwise.
Hoarding by a family member or a friend can certainly be irritating , but like many other things it may not be harmful unless it creates health or fire and safety problems. However as most serious hoarders tend to become worse as they get older I can understand your concern about your daughters hoarding. Especially if there are fire or health concerns. Electrical fires can be started when hoarding covers up and then over time wears electrical cords. Any fire that gets started can be especially hard to put out as the fire can keep going under thick layers of junk. Mould can also be a worry if food or dampness is involved.
Unfortunately that doesn't answer your question Dragonfly, perhaps someone else has some better ideas. In the meantime you can try reading at
http://www.ementalhealth.ca/Simcoe-County/Hoarding/index.php?m=article&ID=13330 . This article has some good tips. You might also want to read
http://www.cdnfirefighter.com/structural/collecting-trouble-9843 for background info. Take Care. paul m
p.s. to Peter. I tend to be a clutterer too.