Just pop back to your homestead and go to the hall of heroes. She'll be right there.
BOTH of my companions pulled that on me. Excuse me for having glorious magic spells, ya jerks. It's kinda funny, too, because they agree to join you just the same as if you'd asked them nicely to wait for you. No fuss, no changes in behavior. It's almost like they throw a little hissy fit and then get over it 30 seconds later. XD
