However, I just lost about 43lbs & am lighter than I have been in years. BUT it's due to a complete change of diet rather than dieting, per se...and I had to be 'in the zone' to do it. No amount of nagging or teasing made the slightest difference.
Therefore, I reckon that the OP's g/f will lose the excess when she's good & ready NOT before!
And nothing and nobody will help, teasing, support, nagging. It first takes serious introspection. Some people never get out of the obesity trap.