Why are you concerned about her both being bored and also not being able to handle being bored? If you're worried about her being bored because she's gifted, holding her back a year isn't going to help - instead I'd be investigating what options you have for schooling in your area - is there a gifted program starting in K? Are there charter schools with alternate philosophies or curriculums that might provide good intellectual stimulation or creative/project-based learning or self-pacing etc? How good is your neighborhood school?
If you're worried because she doesn't handle boredom well now - what types of situations are problematic? Knowing a little bit about the details might help us a bit in answering. I found that at that age, a lot of behavior was situational for my kids. That doesn't mean we didn't have problems with boredom in school, just meant that what was challenging before they entered school didn't necessarily predict what happened when they actually were in school.
Best wishes,
polarbear
