I think she dislikes her, she has shaded her multiple times and I'm pretty sure Nicki knows but she definitely wouldn't respond because she knows she'll get back lash for it.
What? I doubt it. I've never seen Gaga say anything bad about Nicki. Frankly, I've never seen Gaga say anything about Nicki at all. If anything, I'm sure she likes her. Gaga never says any mean things about other celebs.
But she followed Fendi on Twitter, a producer from Nicki's previous years in the game (2007-2008), who has stated his disliking for her. She must've actually done a lot of research on Nicki to even know who Fendi is.
Hate is a strong word. I just don't think Gaga has any use to reference or acknowledge Nicki. Doesn't mean she dislikes her, it just means Gaga doesn't need to or has no desire to.