Typically I get the "but what about the gaps for this year" or some similar comment about what we are skipping over and missing by going ahead to chemistry, biology and physics. Am I wrong in believing that studying these will cover whatever gaps?
Don't worry about gaps. Every child, no matter what their educational environment is, has gaps in their education. Most often when I get this comment, it is from people who are "box checkers" - they want to go down a neat list and check things off as "done" so that they can move on. Just smile and say "I'm sure she'll pick that up when she needs it." If people get truly obnoxious, you can be more direct and day "She's above grade level, why would I want to move her down?"
Lots of people are uncomfortable with something that is outside the norm and you have hit two here with giftedness and homeschooling. I wouldn't worry about it. The more experience you have with homeschooling, the easier answering questions will be.
Learn on!
