Busy, but just a point or two.
IANA anything. But IMO there are several types of hoarders.
If she hoards stuff like the daily paper and soup cans and milk jugs you/she are doomed unless she stops cold turkey/gets a professional. Otherwise, you clear the house and six months its full again.
If she hoards stuff she buys, stuff folks give to her, or the occasional momento (theater ticket…) you have some hope. If you totally clear it out, get her to buy less crap (and given she hoards money that will probably help), make sure few people GIVE her stuff, and try to make the momento stuff small, manageable and infrequent, then if you clear out the house it might be years, if not decades before it gets this bad again, even if therapy didnt work. So, at least, you’ve bought years of peace rather than months.
Its kind of like some druggies/alcholics. Some are gonna get the fix however and as soon as they can even if its hard to get . Others manage quite well as long as the stuff isnt easily at hand…