Maybe, or maybe she's afraid she will forget or whole feelings thing could collide with her Godess goals and so on
Shadowheart outright tells you herself she worships a goddess of LOSS.
Yes. It conflicts. She will have to decide which is more important in the end or otherwise find some way to balance the two.
It's not that she WANTS to be alone. It's that she's USED to it. Buuuuuut, if you never give up on her, even if she's the most hostile toxic person on earth, maybe, just maybe she'll come around.
I face "Darth Vader" events daily. I'm Luke Skywalker. Like him, I never give up. Ever. Once I care, it's for life. Turn on me? I'll try to understand. Then I'll make sure we have fun doing what you want. But I'm the one getting you to want to do it.
That's what Shadowheart really needs. Support. She's lost, she's confused. She can't even remember herself. That's a lot of pressure on anyone interested in her. You have to REALLY show you're capable. Same with Lae'zel, except where Lae'zel already knows the "signs of being capable", Shadowheart is less aware and misses this. You basically have to be her teacher.