Can you just ask her if she would like them? I've done this, I explained that I have some "nice" clothes to give away, and asked "do you need anymore clothes, or do you have enough already?" One time I handed over the bundle at the same time as a "proper" gift of new clothes/a toy as I was invited to her baby shower, but another time it was someone I didnt know so well so I just gave her the second hand clothes.
One of the women at DD2's crèche is about to go on maternity leave for her first baby. She has regularly commented on DD's clothes - more particularly the hand knitted stuff (done by me & also gifts from friends). We talked recently about how she loves hand knit stuff but has no knitters in her family/friends.
I was planning to knit something small for the baby. The thing is, I have some lovely pieces that DD has grown out of, and as we've moved away from family & friends I have nobody to pass them on to.
I was thinking of bundling them up and offering them to her - kind of "you said you liked them, they'd go to the charity shop otherwise". Or would that be weird seeing as I only know her through DD's crèche?