>>724808656
I think ideally they would get along, but the way Ralsei has addressed her makes me think that her getting involved with the Dark World stuff is Bad
Noelle implicitly plays some role in The Prophecy but Ralsei doesn't seem to want her in Castle Town, despite her nominally being an ally. He hasn't made a room for her, he hasn't encouraged Susie to invite her even though he talks about wanting her to make "real friends." He knows that Noelle likes Susie but only brings this up to discourage (You) from having Kris pursue Noelle, which is something he DEFINITELY doesn't want to happen.
Outside of real story stuff, you can also imagine that he might feel threatened and even jealous of Noelle's similarity to his role, in the party and in their friend group. Noelle for her part is mainly fixated on the fact that he looks like Asriel, which can be another fun angle to play with.