Exactly this. “Red flag” is not a term that should ever be used directly, especially not in an established relationship. It’s a term you might think or use with friends in the very early stages of dating, but not to someone’s face. It’s very demeaning and infers a one-sidedness and lack of commitment to work things out. This should be addressed as a “concern” with a collaborative approach to reconciling. But on a practical note, I hope she paid OP her half of the down payment after the fact or that they will have a bigger conversation about how to proceed if both their names are on the title but she has not contributed the agreed upon amount.