My mom will change her clothes 3 times a day. They're not dirty or soiled, she just brings them out and puts them on the washer. Thoughts?

What is your mother's routine when changing her clothes? When a family member did that, I realized that she always started with changing her socks. So I hid the extra socks and only left one extra pair available. Such a small change really did the trick.

Just hang them back up and put them in her closet or dresser. Or when she brings in the next bundle of clothes hand her the hangers from the day before and ask if she could put them away.
If it is really getting to be a bother limit the number of clothes she has to select from at any given time.

As Riverdale stated below, most people deal with the opposite problem, where their loved one won't take off their dirty, sometimes filthy clothes after weeks of wearing them. I'd much rather have your problem if given my druthers. If they're really not dirty, just hang or fold them back up and put them back where they belong.

Conside the reverse which is what most have to deal with. My mother's clothes are routinely taken to be washed now that she is in nursing. When she was in AL before Covid I had to plead to take a sweater that I knew I would wash with more care and not lose. As long as she has enough clothes you don't have to wash them every day just because they are there.