V.W.
Does she wake up EVERY night? Or only on the nights that she happens to stay dry?
If she is not waking up every night, and she is having accidents on the nights she isn't waking up, then you can surmise that she isn't waking up every time, and more time will likely solve it. I am not sure I would bother with an alarm if she is sometime waking and sometimes not.
If, however, she is waking up every night, and using the potty each time she wakes, and is also having accidents on the nights she is using the potty in the middle of the night, that would concern me. Most kids, by 6 yrs old, have a bladder large enough that one nighttime peeing session is enough to get them through the rest of the night. If she is waking up multiple times and using the bathroom and is STILL wetting on those nights... I would definitely talk to her pediatrician about that and see what he says about being concerned that it is something medical, and not just an age/normal growth thing.