I've got an aging relative who has been happily paying Full Fare on flights from LHR to PBI and then using miles to upgrade to First/Business Class. She has no status, but she does have quite a few miles in hand, and the Full Fare nets her extra miles.

She wants to expand her flight this year to include a stop in YYZ on her way back to LHR. Normally she has to change flights at EWR on the way, so she thinks she can fly PBI-EWR-YYZ.

With CO joining Star Alliance does anyone know if she will be able to use AC on the YYZ-LHR sector or have to go back to EWR and fly CO?

Will her upgrade apply across the Star Alliance too?

thanks for any help