Really, when you think about it, shortstack fem-Mikey actually makes a lot of sense if you're featuring busty rat-MILF Splinter. After all, the turtles became what they are by the Mutagen fusing their DNA with human DNA, right? Well, whose DNA was the source? It was Hamato Yoshi (or Hamato Kiriko, or whatever fem!Splinter's human name was). So, logically, if Splinter has big-titty genes, those genes would be likely to pass on to at least one turtle.
Of course, when you think about it like that, it suggests that even in canon, if you did a genetic comparison between Splinter and the turtles, the turtles would register as Splinter's biological offspring and as being at least half-biological siblings, since they're all linked by their shared human DNA.