maybe you can get her a heart ring to go with the necklace....that'd be cute....but if you think there's too much tifffany heart out there, then other styles that are suggested in here are great options too...
Oh...you already got one...I was going to suggest this!!! I saw it at Wal-Mart (I know, I know...but it is so pretty)...and you can't beat the price ($79.97). Comes in different colors too!!!