What do you mean by "really good at not wetting the bed"? Has she NEVER wet it? Or does that mean "not usually, but occasionally, once in a while"? My daughter, now almost 7, has wet the bed a grand total (I swear) of about 3 times. EVER. She was completely out of diapers way before her 3rd b.day... even at night. If SHE suddenly wet the bed I would be EXTREMELY concerned. My son, on the other hand, (almost 10) has had sporadic issues at night from the beginning (he is a VERY hard sleeper, talks in his sleep, and even has gotten up and walked in his sleep before). He wore pull-ups to bed until he was close to 4... and then, I had to wake him up just before I went to bed for the night (around 11:00 pm) to take him one last time... These days, he will go MONTHS without any incident, and then, BOOM. 3x in one week, he'll wet the bed. Maybe he is way overtired... drank ALOT last few hours before bed.... whatever. Just last week he wet. He said he dreamed he was using the bathroom (toilet)... I can remember having dreams like that as a child and waking while "using the bathroom"...
If your daughter is like my daughter, I would call the doc and ask for an appt for a UTI check, unless you know of something that she might be stressed out about that could have caused it (a move, an argument with a friend, a friend moving away, some big upcoming event or trip, something going on at school -check with her teacher if she's in kindergarten, feeling like she disappointed you in some way, etc).
If she is like my son, then I wouldn't worry too much about it, nor make a big deal out of it. It happens. Ask her to be sure to let you know first thing so that you can help her get cleaned up, and show her where to put her wet clothes (the bathtub is where I have my son put his). His accidents always seem to come in spurts... maybe it is a growth spurt thing, too? I haven't figured that part out myself...