There are quite a few vendors in the marketplace here. I've been mixing my own from the start, so I can't advise on the pre-mixed vendors, but there are many threads on the different brands.
Get a bit of a choice - sometimes you can be surprised which flavours you like best. I got loads of concentrates of flavours I love to eat, but found that ones I got less of were great to vape.
Some flavours are tank crackers (threads on these), so best to avoid those until she progresses to a pyrex tank.
Personally, I love the butterscotch & maple flavours. Grape was a surprise favourite. Though I really like cherry, I haven't found a cherry vape yet with much flavour. Banana comes through well, but some of these can be tank crackers. Pineapple and mango also seem to come through well. Very much a personal thing - I've never used tobacco flavours (which I find helps with getting off the fags, as the real thing becomes a disappointment when you've got used to inhaling plumes of coffee maple or something - but that might just be me)