This app was mentioned in 7 comments, with an average of 1.14 upvotes
I'm using Nextplus to generate a virtual number: https://play.google.com/store/apps/details?id=me.nextplus.smsfreetext.phonecalls
I think you need to make one call to activate the number for receiving a SMS. I used it to make a WhatsApp account
Try Nextplus. It gives US number. Not sure abt being undetectable as virtual though, but doesn't hurt to try as it's free
have you thought about having her download another app to give her a phone number? I had an iPod only in the good old days and I used NextPlus to talk to my friends when iMessage didn't work