I wasn’t there and there isn’t much info on what was said. Was she being nasty? Dismissive? Ignorant? You can be the judge of that. Tell her (if you haven’t already) that you feel like your stutter is holding you back and you require more patience from her. Her reaction to that should tell you whether or not you want to continue dating her. It’s difficult for fluent speakers to put themselves in our shoes, tell her how you feel (even if it’s in a text). I don’t what she said to make you feel like a loser but if that happens a lot, end the relationship.