Absolutely use a tug or ball on string. Though that type of reward takes longer than popping a treat. So you don't want to tug for very long, or the reason for the reward will be lost.
Put Rain in drive/ teasing her up with the toy before you go into your training mode, then ask for some positions or circles, turns, ups. Use a key word/phrase when you work on that. I use "are you ready" or "ready?"
Your dog should then offer the behaviors when you use the key phrase.
Once your dog is conditioned to that word the drive state comes up naturally when hearing it.
This is a method I've learned from working with Bridget Carlsen(though there is more to it!) Look at Michael Ellis's clips on building drive or go on Bridget Carlsen's site for some video clips.
Is Rain not motivated by food naturally, or is it due to stress in the training environment?
I'd also crate before and after every training session(afterwards especially so Rain can process what she just learned)