Face it, you strung her along. Even ignoring all the other fishiness in this situation, any way you slice it stringing her along like that was not right.
You have TONS of contradictions in your posts (YT won't let me quote them all here, so I will have to paraphrase, people can read the thread for the actual posts themselves):
You "didn't know she wanted her", when her mails clearly indicated she did.
The biggest contradiction I see is your switch from "first come, first serve" attitude to, "oh, well I picked the best home." However, you repeatedly said the new owner was interested in her FIRST and that is why she got her. That is not properly evaluating homes IMO.
You didn't have the information available and had to talk to your vet, but then apparently you had it for the other buyer's questions.
The list of contradictions goes on...
Then you resorted to an unprofessional attitude and name calling!
In my opinion, you handled this entire situation quite poorly. I am sure Izzy will be happy where she is, but that still does not make this behavior or treatment right.