Flowers would probably be the obvious choice. Something in a 'cheery, hope things get better for you' kind of bouquet as opposed to going for the romantic bunch just yet. The card should also strictly be about cheering her up. Show you care about her feelings as opposed to feeling her.... Oops, sorry I slipped for a moment there.
Shortly thereafter, the old spontaneous carefully timed "Hey, you looked like you needed a coffee." when you notice she is having a particularly bad day.
This opens the perfect opportunity to test the waters with, "I hope today is much better for you than yesterday. Here are some chocolates to help get it started..." Again, the small sampler sized boxes with a little card. A full box might be trying too hard still at this point.
If she stops smiling when she thanks you, then it's time to pull out, but again nothing to lose.
I'm Riffing. People usually stop me when I'm riffing. Or carry on without me. That's also an option.