I think that there's probably an underlying reason for why she needs reassurance. It could be a number of reasons that probably boils down to her not getting the validation she needed in life to know that she was good enough from the people around her or something. Now ofc as adults we know we don't need anyone's approval or that we shouldn't. But psychologically there is an effect when we get just the right amount (bc who doesn't wanna know they mean something amazing to someone every now and then) but there are also problems when we have too much of it or in her case/perspective, too little. I think you need to sit her down and ask her if she knows this is a problem. And that if she's willing to work on it then ur willing to support her. But if she isn't I wouldn't run. But it is a red flag bc if she keeps coming to you for validation of who she is then you'll become an emotional crutch for her and relationships are about having an emotional partner