What if you cut squares of red, pink and white (or other colors!) tissue paper and cut 2 hearts out of clear contact paper. Peel the paper off one heart and let her stick the tissue paper all over. Then peel the paper off the other heart and place on top. You can punch a hole and hang a string on it if you want and it's like a sun catcher. Or just leave it as is!
You can also just have her put tissue paper on the contact paper and then cut out the heart after it's completed.
If she'll paint with a paintbrush, you can write a message in white crayon, then have her watercolor paint over the paper. The message shows through.
Or, cut a coffee filter into a heart. Have her scribble with markers on it. When you wet it (a spray bottle works best, but you can also use a damp paper towel), the water runs and looks like stained glass.
DD used to have major issues with paint (or anything that resulted in messy hands) so we'd give her a paintbrush. She did really well with it, and has since grown out of the messy hands issue so she paints on her hands with the paintbrush before finger painting, so maybe that would work?
What about an inexpensive frame made of cardboard or thick paper that she paints and you put a picture of her with them in it? You can add heart stickers to make it more Valentine-y.
Quality time with the grandparents? Some kind of specific activity like the zoo if just hanging out doesn't work.
Maybe that's crap, but that's our Vday gift. I put the kids on a plane and here we are. Last year, we saw the ILs the week of V-day. We don't give the grandparents actual gifts for Valentine's day.