Your friend should be able to get a refund:
"Seat purchase value is refundable in case of involuntary changes to your seat due to safety, security or operational reasons"
Or I would expect also be able to select a new seat:
"Changes are permitted on the same flight/routing"
Here are the full T&Cs:
https://www.qatarairways.com/en-us/c...rred-seat.html