In this scenario it's too high. She sounds like an entitled, unappreciative, bitch.
Sometimes I wish we didn't have a tipping culture in the U.S. it leads to this sense of entitlement on the server's part and sometimes awkward obligation on the patron's part.
Yes, one should tip at least 15% but that's a courtesy... there are some people would wouldn't tip her at all.
Even then, who's to say she just didn't do a lousy job? Some people believe in tipping well no matter what. Listen, if my server sucks I'm gonna gradually drop the percentage.