@Florence649 I'm not sure what is so off-putting to you about this reservation. I don't find it that weird that she amended the reservation from 6 to 8- people's plans do change sometimes. She at least told you, rather than just show up with extra guests. And that she is willing to pay for all 14 nights and only stay for 10 doesn't seem that disturbing, either. She might just really like your place, and the extra 1200, split between 8 adults, may not be big deal to them.
Maybe you are getting some other strange feeling from her? I do think you should follow your instincts, as they usually prove to be right. If this was an Instant Book, you could cancel it by saying you're uncomfortable with the booking. If it was an accepted request, you might have a harder time getting a penalty-free cancellation. If she was trying to bring more people than your maximum (or do specifically state only up to 6 adults?), or was being pushy about a discount for the unused days, it would be easier, but I can't think of any strong basis that Airbnb would let you cancel for just for what you've mentioned.