For this pair I am using Bernat Satin Sport in a colourway called Seashore, but for the next pair (which are to be for me I am told) I am going to buy some Cascade Fixation if I can find a nice red colourway. I am using US #3 dpn's. They are about the thickness of a sport sock, if you understand what I mean.
The Cascade Fixation has a bit of elastic in it, so it will keep the socks up where you put them once you have them on. I was told it was machine washable, but then someone in here told me it was not, and then someone else told me it was again. I am hoping it is washable, even if I have to lay flat to dry.
Good luck finding something she will like. Try Mary Maxim, they have a ton of sock yarns and are bound to have something hypoallergenic (I hope, because that is where I shall end up too).
I love to give homemade gifts... which one of my kids do you want?
Find our "Canadian Oddball Blanket KAL" on Ravelry as: OddballBlankets