I would schedule her to be spayed asap. By allowing her to go through a cycle she has an increased chance for mammary tumors as she gets older. You also have the extra work of "clean up" as it can be quite messy. Females generally do get quite moody at this time, especially the first one. There is also that slight possibility that she could accidently get bred. Not worth any of those risks.
I agree with Sam, however, for some reason in my area the vets will not spay a dog until it is at least 6 months old AND has gone through their first heat... dumb huh?!?! I've always gotten my dogs spayed as early as possible, so this change in policy makes no sense to me.
Anyway...hopefully your vet can go ahead and do the procedure. Just for informational purposes, my Heidi went into heat for the first time at about 9 months old. But I guess, like humans, it's different for every breed and each individual dog. Heidi just got spayed last Thursday (she's 10 months old now) and I am very relieved. :) Good luck!