I know you asked about shoes rather than general wardrobe- and I’m sure DD is too smart to make this error- but please tell her to think a bit about her clothes! So many folks go on vacation to Thailand and treat it as one big beach- wearing bikini tops and short-shorts everywhere. SO NOT appropriate! (Unless she will actually be on a beach the whole time.)
Bangkok is like the New York City of Southeast Asia, so sophisticated and edgy clothing is great; sloppy, not so much. And in more remote provinces or small villages, skimpy clothing is seen as very disrespectful. She’ll be received much better if she chooses lightweight, breathable tops that cover bust and upper arms, and bottoms that are looser and longer (good thing longer shorts, culottes and longer skirts are in). This type of bottom will also work better for getting on and off boats, moto-taxis and tuktuks.
Hope that helps! She will have a blast.