For only dating a couple months? Hmmm....Maybe a pair of silver or gold hoop earings (whichever she wears more). Or a nice bracelet in the same. Also a Fossil or Guess watch. Why?
All of it is jewelry but none of it symbolizes the same things a "ring" would. Yet each could be worn daily to remind her of YOU.

I've received all three from Duff and have charished everything - even knowing they weren't too expensive, it was the idea of him picking them out on his own....carefully and with the thought of me keeping them long term. Pretty cool i.m.o.
I love the bracelet I got from Duff last year. I haven't removed it once since last Christmas and am thankful of him every day when I see it.

Good luck.

Nic