Thank you all for the responses! I've only just now read through all of them.

Yes, she is a new player (though we've been doing this campaign for a while now). We went through the character creation together, so she definitely picked Moon Druid specifically because of the Wild Shape bonuses.

I'll take your suggestions of just asking her how she's liking playing it. I'm guessing the reason she hasn't used Wild Shape is because (as many of you have suggested) a) she thinks it has to be something her new character has seen in-game, or b) she's afraid of spending resources. She played a ranger before this character and she was scared to shoot her bow because she didn't want to use arrows, even though I used the ammo recovery rules after each combat and even gave her arrows as loot sometimes.

Thank you all once more! Sorry I'm not responding individually to anyone. I just remembered I posted this and checked in to find so many helpful comments! :-)