I seem to be in the minority here, but I would think it's probably OK in small amounts. I have trouble taking the warning about pregnant/nursing mothers seriously, since people in S. America have been consuming it for centuries. I give it to ds (4 yo, almost 5) in small amounts. He has diabetes, and there's no way I'm giving him artificial sweeteners! I usually use it to supplement other natural sweeteners (like raw honey or agave nectar, and sometimes I use glycerin instead) to make things lower carb.
All the studies I have seen written up about stevia describe giving huge amounts to the animals. And even then, many of them say it's safe (a few say there may be problems, but if you look carefully, there's usually a question about how the study was conducted -- there may be the same kinds of questions about the positive studies, too, I can't remember). I'm reserving final judgement, but do feel that it's probably OK in small amounts (and who needs large amounts of stevia? It's soooo sweet), and we use it sparingly.
Mostly though, the sweet things we eat are fresh fruit. Could you maybe make a smoothie for her instead of adding a sweetener?