Frontier is the first Macross series to have the events in Zero part of its background 'history' so Mao would not be referenced anywhere else.
As for the 'doctor'/professor reference, your guess is as good as mine due to the extremely brief reference to it and most likely alludes to things she did after Zero. Just the start of a thread we'll eventually see out hopefully.>>12353578
Don't forget that surnames are traditionally (in a patriarchal society) carried by the males of a family lineage. Mao would be very unlikely to pass down her family name, unless she marries a Zentradi who AFAIK do not have family names and it doesn't seem that Sheryl is part Zentradi... wait a second, wasn't Ranka 1/4 Zentradi which means one of her grandparents were Zentradi? WoooooOOOooo!
If the family name and the allusion that Ranka is a descendent of Mao turn out to be correct assumptions, Ranka and Sheryl would be cousins. (Ranka's mother would be Mao's daughter and Sheryl's father would be Mao's son following patriarchal name lineage)