to feel taken for granted?

Don't make assumptions.
Perhaps when she gets home, mention the laundry and tell her where the washing machine is, if she needs instructions I'm sure you can help. But do NOT do it for her.

I might be a bit miffed if the clothing had just been left in a pile on floor, as this was a pet peeve of mine, when children were at home. My middle DS often pops in with washing usually white T-shirts or shirts that has a mark that didn’t come out when he tried to wash it. I don’t mind although the last four pushed my eyesight to the limit as the marks weren’t obvious. He has two flaws he likes expensive clothes, ( he pays so not an issue) and he’s very particular anything white has to be brilliant white, even his trainers. A volunteer in one of our local charity shops used to be thrilled when I showed up with the bag of marked trainers as her son worn the same size and he was thrilled to get almost new trainers for a few pounds.

Wouldn’t bother me, would say when we next spoke, lazy mare, I’ve picked your washing up, all laundered for when you next here, miss you already!

I do not agree that it is normal for grown-up children to revert to teenage standards when visiting their parents. Neither my sister nor I did so, or would have got away with it if we tried, nor have our children done this.

If someone leaves clothes behind, then it is actually theft if you appropriate them for your own use, throw them out, or give them to charity, irrespective of who the original owner of the clothes is.

If it is bedlinen and towels, I would mention casually in my next letter or text to my daughter, that I fortunately found the dirty linen she had forgotten to put in the dirty clothes basket before it stank and leave it at that. If it is her clothes, mention that she forgot them, and that you have washed them and put them into a plastic bag or some other suitable container to await her next visit.

If it's clothes behind the door then maybe she left them by mistake, my grandson always manages to leave something behind. If it's bedlinen I would not expect any visitor to wash it themselves, I am grateful if they strip the bed.

I would machine wash but not iron the clothes, so they are not ready to wear when she returns, which will perhaps make the point that she is taking advantage of your good nature.

Do not see the problem at all. They are clothes she keeps at your house for next visit. I would just wash and iron them and put them away ready for next visit and be very glad she visited.

You doing her washing usually goes smoothly, I would think she simply forgot to put them where they were supposed to be.

OP, am also eagerly awaiting my DD to visit from New York and I always ask her ..Do you have any washing ..before she leaves again…think maybe you were overly tired when you started this post but I appreciate my DD wanting to visit as it’s quite an expense- in fact, and am quite sad every time she leaves ..so washing behind the door not an issue 😊

Reframe it as a compliment. She can still be the daughter in your house and you will look after her as you always have. Let it go. Not worth getting miffed about it.

Throw her clothes awayclearly she desn't want them.and launder the ed linen

I would just wash them and put them away until you see her again. At least you got a visit which is more than I get.

I would text her and say are those clothes for throwing out or was it that you wanted me to wash them? It feels a bit rude to me, to just leave them without saying anything.