Glad it all worked out! I'm actually in a kind of similar dilemma; a friend from HS, who I reconnected with a few years ago, is having a very casual get-together, that she planned, to celebrate her birthday. Nothing fancy, and as we are all turning the big five 0, or have already, I suspect she just wants something quiet and low key. Fine by me, i'm the same way.
But since it IS her birthday, and while not really an official party or celebration, I still feel like i need to give some sort of small gift. It just kind of goes against my nature not to. She doesn't drink otherwise a nice bottle of wine would have been perfect. So I asked another friend who she's closer to, who said not really that kind of party, no need etc. And we are all bringing munchies, and will literally hang out in her yard, and talk and whatnot.
So my friend who I asked, said well, if you must, you know she's very practical, so a gift card to this or that would be nice. So i said fine, i'll get a small one, and hide it in a card
Problem solved because hopefully when she opens it, later on, I'll be gone
so she can't refuse.