Is the problem that she doens't know if she is dreaming or not?

Reality checks work, in that case.

Watches and mirrors don't work in dreams.

Tell her to glance at a digital clock or watch. Wait a few seconds and then do it again. If the text or time inexplicably changes, then she is in fact dreaming.

With respect to mirrors, tell her to look in a mirror. If the image is inexplicably distorted or bizarre, it's a dream.