I am converting to Judaism (not for a romantic partner but because I am called to it) and the "not allowed at holidays" thing threw me, too. I've definitely attended holiday celebrations in people's homes and at synagogues; I've been called by a Modern Orthodox rabbi (who knew I am converting but not converted) to dress the Torah. This makes me wonder if LW's love interest is a member of one of the more extreme (dare I say, "cultish"?) sects of Orthodox Judaism or if her boyfriend's family is going to be nasty to her even if she does convert.

As for converting, LW should really ask herself if she'd be okay converting if her boyfriend dropped dead tomorrow. Because if the answer is "no" then she really should reconsider.
Any rabbi will ask her the same question. Chabad has a whole agony aunt letter about this from the boyfriend's perspective: No, you cannot convert her. … She must do that herself. And it must not be a conversion either, but a giur. Meaning that she must come, as did Ruth, on her own volition, "because your people are my people and your G‑d is my G‑d." If it is in any other way, it is a lie, and certainly you do not wish upon yourself the cruelty to force another to live a lie.

I guess it seems strange that LW does not know this? She's gone through the effort of kashering her kitchen(!!) but nobody's told her this very basic information about conversion?