I'm so sorry this is happening. I think it is because you shut both cats in the bedroom when the maintenance people were there. Galaxy simply didn't want her daily life interfered with, and after she had peed once on your bed she thought... oh, this works well. Ugh! Perhaps she didn't want to use Sparkler's litter box for some reason. I really hope putting an extra litter box for her will solve the problem, but better yet, is if she goes back to peeing in her own outside the bedroom.

If none of it works, you could put plastic over the bed when you're not there, but that's no fun.

Best of luck solving it! Give her some extra loving, too.