For the OP:
I have two M&P15-22s and they are awesome. Lost of fun and light if that is an issue.
Re building an AR upper (since you already have the lower), there are several Labor Day sales going on right now.
AIM surplus has a sale going on including FAXON and Ballistjc advantage AR barrels and other parts. ALG / Geissele also has 20% off for Labor Day - ALG rail and a BA or FAXON pencil barrel would be a good start to your GF痴 new upper.
https://www.aimsurplus.com/catalog.a...Day+2018+Sale!