Proper Tip For Panda To Give Hairstylist?

Let's try this again. I am a male in my 50s with hair that is thinning but still full. I live in Los Angeles and have had same hairstylist for years. She had been at $18 for a basic men's cut (no shampoo, etc) for years, until raising it to $23 when I just went in last week. So my question is, what is the appropriate tip amount? I really do like her and she does an excellent job. I would love to hear from everyone, including any hairstylists, on what an appropriate tip would be for my $23 haircut.