I have one more theory, it may ou may not make sense, but this has been in the back of my mind for a while.
In one of the options on her Instagram, Rainbow posted about Vamppreg, but, thinking now, it may not be related to mpreg.
So, having in mind that Fiona may have already married Nicodemus when Scattered Showers happens, maybe the pregnant one is her 👀.
Like, I have this theory in my mind, that maybe male vampires are able to get people pregnant, but female vampires aren't because as they body heals fast, a pregnancy is impossible.
(but maybe if the vampire one is a "vegetarian" they may can have a baby)
And Fiona probably is in her mid-40's late 40's, it's harder but not impossible for her to get pregnant.
I know it sounds crazy, but makes a lot of sense I'm my head