YABU
you are entitled to your opinion, but other than expressing your concerns and explaining why you feel that way- which it sounds like you have done- there is nothing more you can or should do and is where it ends. Anything more is over-reach on your part.
Your daughter is, at 24, an adult who is allowed to make her own decisions, regardless of her mother’s views. You need to take a step back and accept her decision. It may be that the relationship is a disaster, but that is her mistake to make. All you can do is be sure she knows you will be there for her if she needs you. Push her too far and all you will do is drive a wedge between you because you are over-stepping boundaries, and the result if that will be a distancing of your relationship (in some ways) and she will find it harder to seek your support if she does need it.
As a parent you have no right to control your adult children’s lives- you seem to feel you have some right of veto on who she can have a relationship with, but you absolutely do not have that. Do you feel the same about other aspects of her life- e.g. who her friends are, her career etc? In all honesty, as a parent of an adult you do need to learn to respect her autonomy and right to forge her own path in life- she’s is going to make mistakes and mess up, as we all do. Hopefully, not too often and not too seriously- but they are her mistakes to make. Your role as her parent is to offer advice- preferably when your opinion is asked, for the most part- and offer support where necessary.
I speak as the child of a parent who did not respect my boundaries and felt they had a right to a say on how I lived my life (including who was, and who was not, a suitable romantic partner). I deeply resented them and felt absolutely undermined- it felt like they did respect me, did not value my opinions and did not trust me to know what I wanted from life or to make good decisions by myself. So, I simply kept them at arms length. I saw them less often, most contact was by phone/messages and I did not discuss my life with them in any great detail. In essence, our relationship became very superficial. I did not trust them to respect me or my boundaries, so I acted accordingly. I know they were very hurt, because from their perspective they were simply trying to help/make sure I was happy/did not do something I’d later regret. I’m sure that was, partly, the case- but I also think it was because they still failed to see me as an adult who had a right to make my own decisions, but rather felt they did have the right to enforce their views because I was their child (I think they felt the it was ok to try and control me because they were trying to make sure I was safe/happy/not making a mistake). The truth is that I did not need protecting from myself, I needed a parent who would be honest with their opinions but ultimately able to put those aside and support me (or at least respect me enough to accept my decision) where we differed. obviously, I don’t mean blind support, e.g. with something illegal etc. We have repaired our relationship over the years but it hasn’t been quick or easy.
Your attitude of “she just won’t listen!” reminds me very much of what I was on the receiving end of. It’s infuriating to be told that you just aren’t listening because you don’t agree with their opinion and/or won’t cave in to demands to change your decisions. The answer is- she has, no doubt, listened and understands what you think but disagrees with your point of view. And has decided to pursue this relationship because it is what she wants to do. You’ve told her what you think, now you should respect her right to make decisions about her own life. If you don’t, you may damage your relationship with your daughter.