I received birthday and various holiday cards my whole time as a JW. My kids did as well. This might be a different slant on this, but what the cards did for me was keep alive a little gnawing thing in my head and heart. It felt so NICE to be remembered with a card; I was thought of and loved. The gnawing thing was the thought "how can this be "bad"?!"... and I always wished that I *could* give cards, gifts or at the very least acknowledge someone on their birthday or return a holiday greeting -- it was just a nice, normal HUMAN thing to do. I never really felt 'right' turning off the natural love as expressed in cards and good wishes.
So if you do give her a card, I would give her one from your heart. Soppy Hallmark that makes your eyes well up? That's how I know I found the 'perfect' card -- if I'm sniffing away in the card aisle. If she's 'stumbled' or offended, it's really up to her to tell you... but if she hasn't said to NOT give her one, then by all means express your friendship to her. :)
Just my 2c :)
~merfi