Most Helpful Girl
Just a simple happy birthday message would be good, though I wouldn’t expect anything back if she’s still with her boyfriend.
Most Helpful Guy
Don't. Don't wish her a happy birthday if she has a boyfriend. You will look desperate no matter what and there will be very little doubt of what's going on inside your head. You have to let this go. Don't be looking at a taken woman or you're going to end up waiting way too long and you'll never end up with the right one.