I don't really understand scaling tips past a certain point. The service is generally the same whether it was a $1000 steak or a $20 steak. Unless it goes directly to the chef. Everything else is already compensated by the cost of the meal.
Maybe casually ask her sometime if she needs anything? Listen when she expresses interest in a random gadget, piece of cloth, etc? Notice when she gets frustrated with a task that a tool can help with, or that you can volunteer to manage?
People usually buy gifts they would like, and its so nice she loves it still, but I'd bet she'd be extra happy with a surprise.
I've seen homeschooling moms check out dozens and dozens of kids books at once. Plus you could use multiple cards if you're planning some grand arson demonstration, I guess.
Whoa are we forgetting tax? The internet required to turn on your device for the first time, and download the physical game you bought? Ha!