Curie is glitched for many of us. I can't get Curie to stay at any of my settlements. If I try to send her to one, she just goes back to Vault 81 regardless of what I do. She probably went back there. She stands in front of the doctors office, so that's where I'd look.
This is a glitch that I'm desperately hoping gets fixed in the next patch. I have all of my favorite companions at the same settlement so I can easily switch between them. Curie is one of my favorites as well, and I'd love to be able to have her at my settlement.
It's odd. If I try to send her to Sanctuary, for example, a notification will pop up saying "Curie is going to Sanctuary," but she'll just end up running back to Vault 81. I've tried this at numerous different settlements, tried sending her to the settlement while at that given settlement, tried it while at different settlements, out in the wasteland, while actually at Vault 81...I always get the "Curie is going to Sanctuary" notification, but she won't go there. I've also verified that it wasn't a settlement population issue or charisma issue. A lot of people have had this same issue though, and I'm pretty sure Bethesda is aware of it.
Anyway, check at Vault 81. I bet that's where she's at. You may have missed her when you looked there. If that fails (and you're on PC), use the console command mentioned in the previous post.