Hi @Cait12 ,
No it's not really fair and not particularly professional.
A host should keep their calendar up to date, and not alter it when they get an enquiry. sounds like she has smart pricing on, and the dates have opened up and a rate too low for the season and she hasnt' realised until you enquired.
I"ve been caught out a few times and I"ve always honored the booking because I believe it's the right thing to do
But just so your are aware - and possibly in her defence - the system CAN be very glitchy.
It's possible an airbnb algorithm did something weird and unexpected to her pricing and she only just noticed when you enquired. For example, airbnb once opened up dates on my calendar over xmas new year that I had blocked, for some ridiculous price and the first I knew about it was when I received an instant booking.
Not meaning to be rude, it's also possible that for whatever reason, the host doesn't really want you to stay, and has increased the price accordingly.
If you do find a property with instant book that you really like, within your price range, during a peak holiday time that will be popular and fill up quickly, then you could consider booking with IB and THEN clarifying a few things- (so long as the cancellation policy is anything from strict downwards, then you have the option to cancel without penalty within 48 hours.) It depends what your questions are of course. If they are major questions, then definitely wisest to ask before booking.
Overall though, I would be inclined to agree with you. I would be seriously put out and not inclined to give this host my money. But it's hard to know for sure without knowing the full circumstances from her also.
Good luck finding somewhere nice to stay!