Finding she was just one of many girls, especially a wide range of them, wouldn't be good for her mentally in my mind. She thinks the MC likes her for her, and not just because he will fuck anything with a heartbeat, including family members. The idea that she herself in turn could be loved would be shattered. Or at least that's how it should play out.
I do think she wants a family. Her current family sucks. I just don't think she's looking for a harem family. She's probably already thinking of a wedding dress, a honeymoon with the MC, and adopting kids and a cat and dog.
Disclaimer here in that generally I don't like harems. They feel forced and then there's also a feeling of a cult to them, possibly because they are a feature of some religions and especially cults. And what we're describing here is basically a cult where Nea is love-bombed by the others because she's vulnerable. If she joins, it's either because of her mental health or just because it still beats her current life and she's willing to settle.
Nea needs her own path, at least as an option. Or maybe Luxee can write things so that Nea joins the harem and it makes sense, and isn't just kind of sad because she's settled for far less than she wanted. The other women more or less will all fit into the harem, but then again none of them have the depth of Nea's character, and none of them as desperately need the full attention of someone who loves them and them alone.