You are right! She was also the daughter of Princess Alice and Prince Andrew of Greece.
Yes, she and George Donatus were were first cousins once removed (he being her mother's 1st cousins). He wasn't her uncle. Didn't all the Battenberg/Greek daughters marry relatives of some degree or not? Except maybe Theodora and the Prince of Baden. Sophie even did it twice (and to cousins themselves!
QV--Vicky--William--Victoria Louise--George William (2)
QV--Alfred--Alexandra--Gottfried of Hohenlohe-Langenberg
Forgive me if I've switched Theodora and Margherita, I sometimes have trouble keeping their marriages straight and I'm doing this off the top of my head.