ok, so this might sound almost impossible but I'm trying to get my mother in law to like me. My first task is to try to upgrade her on her trip from London next week.

Is there any GG BUYUP like in continental, to be able to use a SWU or another instrument?

She has an L fare, so upgrading her to W would cost about $200, unfortunately United wants to charge me $250 change fee.

Any other way to upgrade her besides paying the 20K miles plus $500 copay?

GG BUYUP (for continental) - Did you buy a low fare class ticket? Want to buy up to a higher fare class to ensure an upgrade (e.g. Y/B/M or even a true F fare)? Call in to the reservations line and feed them this little ditty and you'll be on your way without having to pay the change fee on your ticket; you'll only pay the fare difference. Sitting in first class has never been easier.