You do realize that any scene with her would take screen time away from any of the actual LIs, right?
You say that as though it's a zero sum game. It's not. We can have both. The full game would need to be a little longer than without her, but we're already all here for the long haul. I would also like to see Eva have more screen time. She intrigues me and I want to know more about her. I know that by now it's probably too late to have another sex scene with her, even though Orion is not yet established as the boyfriend of any character. Annie, almost, but that has not been discussed, and of all the girls Annie so far seems most obviously open to including others in their relationship (based on comments she has made about Dalia and Nancy). This might only extend to ones she has an attraction to. But I'll take friend interactions with Eva, as long as I get more of her.
I also really really want to have a scene where Annie finds out how Orion knows Eva. Annie as I first got to know her, I'd expect shock. But Annie as I know her now, that shock would quickly into "oh, lucky girl!" and admiration that he got to be with Eva and didn't have to pay. As for the others, I don't think most of them would give it much thought. He hadn't so much as kissed any of them when he met Eva. Even Luna shouldn't be upset with him. She's too sweet, so any jealousy she might feel would not last, as long as she knows Eva can never take Orion from her.
Adding her as an LI? No. That wouldn't work now. Keeping her as an interesting side character who pops up here and there, that can.