Any grooming going on in this series was with Rudeus and Sylphiette when they were children. But it was very brief and due to their eventual separation, did not have too much of a long-lasting effect, but it has one nevertheless. You had an adult man in the guise of a child encouraging features and behaviors in a naturally meek girl. They developed a significant codependency that Rudy's parents noticed and corrected by sending him away.

It's a significant driver to why she's the most boring heroine in the entire series. She's meek, demure, and accommodating. Fully boring. Bland wife-servant personality. Bleh.

I support Roxy having her smitten period here because it's already been established that she's an excessively late bloomer due to her disability with her own species which isolates her from her own people and makes her an outcast to her own continent, but a welcome adventurer elsewhere. She has social hangups so it does track that she's finally aware of Rudeus. Others that she has spent substantial time with are like much older siblings to her (even though she is likely older than most humans). It is slowly dawning on her that she's lovestruck, but her main focus is certainly adventuring with a competent person that she gets along with and who can explore magical shit with her without being a creep (the prince she tutored), pervert (the other prince she tutored), asshole (Paul), whore (she doesn't know Elinalise has a path forward and ambition to stay loyal), unhygenic and kinda a weirdo (Geese), no interest in magical stuff (dwarf), or anyone else she's traveled with over the years. Roxy would like that to develop into more, maybe possibly, but she's too stunted to be forward about it so she's playing this card even though everyone around her knows her well enough to see it plain as day.

Rudy just doesn't believe it could be true, so he is Main Protagonist Dense for the purposes of this arc's narrative.

It's a huge stretch to say that she groomed Rudy. She trained him, then left. They stayed in communication like normal close tutor and pupil, though we know that Rudeus developed a complex around her, Roxy didn't and merely remembered him as an exceptional student who helped her get out of an awkward employment and skill development period in her life.

All that said...Eris is still better than both Roxy and especially Sylphie and this series deeply suffers from her lack of presence. Eris' independent attitude and desire for self-betterment is vastly superior to devoted and horny but otherwise Zero Personality Wish Fulfillment Wife and Smitten Late Bloomer Socially Naive Adventurer Roxy.