I can't believe I stumbled upon this thread! I was looking at this exact ring at Nordstrom tonight for my daughter's 21st b-day (Feb. 18). I decided to sleep on it but after seeing this thread I'm convinced it will be the perfect gift. Like the OP I want to get her something memorable and without sounding too corny, I feel like the combination of the rings and the diamond x symbolize hugs and kisses.
Thanks for starting this thread, I hope your daughter loves her ring!!
Your DD will LOVE it!!! What a fantastic b-day gift. And, the symbolism makes it extra special.