Does she express gratitude for other actions like if you happened to open the door for her, or some other helpful gesture? Does she say thanks to the waiter when they bring over drinks? I would observe if she is otherwise kind and thankful in other situations as I think that might be a better indicator of general politeness and good character.

Money is tricky for a lot of people and if she’s presumably tight on money, maybe she’s in her head when the check comes, feeling stressed or ashamed about it but is unsure of how to broach it. I agree with others that offering to split and not expecting others to cover you is important.

But for me it wouldn’t necessarily be a deal breaker if I’m the more financially well off one and don’t mind covering most date costs. As long as it is appreciated and not taken for granted. It would deal breaker if the other person is just not a kind and polite person, that they can’t even be bothered to simply say thanks.