It's a very real possibility. As far as I'm aware, there's not a way to let her inherit your status for upgrade priority like she would on a domestic complimentary upgrade. You should be prepared to give her your seat and enjoy the ride in coach if your upgrade comes through. CLT-LHR is business heavy so it wouldn't be uncommon for the seats to be full of paying passengers (or those who accepted a cash upgrade offer), so none of this may matter anyway.

One other thing to be aware is that if you have Lifetime Platinum but a low number of Loyalty points in the 12 months prior to your trip date, you would also fall behind other Platinum members that have more LPs.