Most Helpful Guy
the most sexy clothes you have, or better darling: Go shopping!!
just ignore her and give your boyfriend a little bit more attention than you usually do.
Most Helpful Girl
Relax here, dear, and Begin your Beguine of going shopping for just the right thing that won't make you look like you are This... Fling.
Being Distasteful is no way to get this 'Not like i am trying hard to impress' off to a First time sizzling step, so make sure it is something Nice, casual, fitting and Appropriate. Perhaps a nice sun dress, no low cut, and even a fitting pair of jeans or a pair of khaki Capri's to the knees is nice. A lovely pair of sandals to show off the toes and while you are at it, make a day at the hair salon to add a nice touch.
Go in, arm in arm, and this will Automatically let her know, who has the Tag on Who now. Be gracious, be polite but Not Obvious where she will Smartly surmise any phony baloney.
If you want to end the madness, maybe it is also time to speak to your SO of blocking her and keeping her at bay by Blocking her from Facebook.
Good luck. xx