I think you should be keeping a score card. There should be different values for an oral event at different times. For example, if you just got back from working out at the gym and you are all grody and your GF performs oral on you, that should count as 2.47 oral points. If either one of you is freshly post-shower and clean as a baby's bottom, that counts as 1 oral point. Oral sex while driving - that's 1.72 points. Keep a spreadsheet handy to keep track of the totals. The goal is to keep the points even.
Seriously, just talk to her. That usually works the best to resolve any bedroom differences.