I have contacted indeed. They did see the error but since the Upgrade by Avios is an "in the system kind of upgrade", not much can be done on their side as there is no more inventory for such Upgrade.

The specifics are those, the flight is from HKG and it's the Cathay planes leased to Qatar. I pressed the upgrade button it showed available for both passengers in the booking, but once I checked out with Avios it gave an error. So I decided to upgrade from the same device at the same time, one using Avios and one QCredit. Mine was the Avios and failed after the payment(tax). The QCredit went through and it upgraded. Once on that flight(only 6 seats available) someone used the upgrade option,it becomes unavailable for an upgrade by Avios for other passengers that have Silver/Gold.

Either way, it will be very awkward for her to fly alone but as discussed with multiple agents, nothing can be done now, not even downgrade unless I cancel the flight.