Oh, this is interesting. I was expecting that they’d spare a bit of time to work out their troubles (well, mostly Luz’s), but perhaps now’s not the time.
(And perhaps Luz needs to work out her troubles alone.)
Although she has plenty of reason to be upset with Luz on a personal level, Amity seems to be prioritising the practical side of the situation. As Emira said before, she has bigger problems.
Amity can’t waste time discussing what they’ll do, and she knows Luz doesn’t have any spells that will be useful in this scenario, so she thinks she’s more likely to be successful on her own without someone else to look out for who can’t really do much to help.
While she is mad that Luz put her siblings in danger, that’s not the only reason she’s insisting on going alone; she’s simply thinking logically.
oh nooo
she’s angry at first and then the energy goes out of her and she just looks... sad and worried...
It can’t be easy for her, even if she thinks she’s making the right decision. She doesn’t know if she’ll be able to manage alone, and the idea of having company is likely comforting. If she thought Luz could do anything, she might be tempted to let her come along, as dangerous as it may be.
But she doesn’t, so she goes with the option that she feels is most likely to keep someone she cares about safe, at the very least. She’s upset with Luz, but she’s worried for her, too.