Re: Best followup text, or is this a lost cause?
You generally shouldn't push for another meetup right away after an interaction. Give it a few days of interaction, and then you can go for it. With that said, the message you are thinking about sending is an absolute no. You don't want to imply that you will wait around for her. In addition, I am sensing a tinge of jealousy in that message. Jealousy is a very AFC thing.
Now that the negative is out of the way, I can give you some of the positives.
Your chances are good. You spat some pretty good alpha game around her, and the man just sat there like a rock. Not a good move on his part. The fact she gave you her number right away is also another good sign. I would say to play off her message as if it was nothing and then continue to flirt and spit some game with her. You can maybe even run a little bf destroyer on her to take down the other guy. Do all of that, and you should be on the right track to getting her.
"There is no better than adversity. Every defeat, every heartbreak, every loss, contains its own seed, its own lesson on how to improve your performance the next time." - Malcolm X