Jerwick, she can get some inexpensive plain t-shirts and tanks for casual nights in the dining room. What does she have for bottoms... skirts/capris/pants? The young girls I saw last week were usually dressed in those flirty, flippy short (mid-thigh) skirts with a nice top and cute sandals (slides, wedges, beaded and flip-flop types). Capris are also appropriate... the girls that wore them seemed to favor the bold floral ones or the low rider khaki ones, which they wore with big belts.
Who knows, maybe she'll have fun dressing up a bit when she sees the other girls doing it!