I got mine a nice necklace with a bird on it. I think there was a small gem in it too. I, like you, didn’t want to do a cross.
The woman who stood up for me at Easter Vigil was a proxy, so I wanted to let her know that I really appreciated that she’d stand up with me last minute. (She was already scheduled to visit her family out of state that day and she drove back early so that she could be my proxy that evening.) And, incidentally, her husband was my husband’s sponsor when he converted. So, I wanted something that reflected how special she (and her family) was to our family. (Her husband was bummed that he had to stay home and watch the kids on Easter Vigil.)
Easter Vigil will be a night you’ll never forget and I think SIL will appreciate the gift. If you think a gift needs to be given, then give it. I just saw it the polite thing to do.