Get a 2nd and 3rd opinion.....I agree with that. They are calling it a mass so I would guess it was solid
vs fluid? I would not rush into surgery, maybe they can wait and repeat the test to see if it has decreased in size, depending on where in her menstrual cycle she is.
Also, if she did have to lose an ovary, there are many women out there that live happy, healthy lives with one ovary and also have families.
Hang in there, let us know what happens after you get the other opinions.