Sounds like early signs of a professional complainer/blamer. While you have to be willing to listen and admit your own faults, you also have to be willing to stand firm upfront otherwise this type of person will walk all over you. I agree with @Ryan Garrison She's an adult, she should have noticed on walk through or simply asked.
The old "I'm blaming you for not telling me what I failed to determine myself", particularly for an easy to remedy, short term issue is a bad sign that she will try to bully you later on. Definitely politely stand firm, don't take the blame but just focus on the solution, and if she doesn't get it after your initial response, offer her early release option (hopefully with with a fee) and let her decide if she want to pay or play.
I had to do this with a recent renter who had a proxy of their choice view my property and then complained of trivial issues (a door being a little too tight, loose thermostat cover, etc) upon taking possession. I stood firm, reminded them that their chosen proxy was allowed as much time to view the property as needed, then told them if they were truly disappointed they could pay the early termination fee. They've been quiet and sugary sweet since :) Good luck.