There is no proof here that girl you saw at the gym perceives herself as having a higher value than you. ---
you don't need to neg her ---
You are the prize.
If you've really only met her once before, then by recognizing her at the gym you have social value by simply being able to pick her out and associating her with past events

. You cannot even assume that she is able to recognize you at the gym - she may have been uncomfortable because she didn't remember you from the party. If she only met you once before at a party, you have to keep in mind she may not be able to place you.
I run into people all the time who I have gamed but do not remember.
---
negs are only to put you on even ground if someone perceives they have a higher social value than you --- you have not presented any kind of a case to indicate she has more social value than you.
if she has a personal trainer then she probably is at the gym to try to change to look of her body - that means she has body issues, negging her is really not a good idea in that case.
if you see a girl you met at a party who is single and at the same gym as you, then it's on!!!:twisted:
you're money - you just have to figure out with her how you share the same social circles as her (neither you nor her really care how you share the same circles, but this builds comfort), then ask her to do something outside of the gym (a day 2) and you're golden!!!