I hate these threads.
What did you give them to her for?
I'm guessing a combination of - to make some space, to save you the bother of selling them/a trip to the charity shop. Which has been achieved whatever she does with them next. If you had donated them to a charity shop, they would have sold them. Would that bother you? Why not that but this does?
Maybe as a nice thing to her, to help her out. Which you could see that you're doing twice - helping her out with some clothing that she needed, and now she's able to get some money that she may need.
Maybe to see the clothes get used again - but they can't keep being worn forever, presumably they are now outgrown, they won't be worn again by her DC. This is the main reason that I can think of that makes sense to be upset by them being sold - if you'd hoped for them to be passed back or passed onto another family child or mutual friend, so you could see the clothes going on to another "life". But in this case you should have said so, not expected her to magically know that was what you wanted.
Used baby clothes do not have a high value especially once postage/petrol/public transport fees are deducted - the value is on somebody's work in collating them and listing them and documenting any variations in condition. It can sometimes be more hassle/expensive to give things away than to sell for a small fee on a local site or vinted etc.
Also I would find it really tricky and stressful to keep track of who gave me what and what all their various wishes for the clothing was. To me that's a horrible expectation to place on somebody and basically means you're not giving them something in good faith, you're doing it for some kind of selfish reason.
I think you should let it go :)