LHR-DOH does have F on some flights. But QR will recalculate the sector LHR-DOH and in the end it will come out more expensive that to upgrade the entire sector in a lower fare. If you think you want to treat her, then do it before you go to the airport.

DOH security does seem rather lax about liquids. They really don't care IMO. But still its a risk as officially you can't take exceeding the normal amounts.

But goodness sake. You're only taking Bailey's. Which is available everywhere in asia! Probably cheaper for you to buy it in Doha really! I'll be passing thru DOH at the end of the month and I can check the prices for you to see if it is worthwhile for you to buy it in the UK!