Classifying female Betta fins types can be very difficult, the shorter than short finnage always looks similar to what you'd expect to see in a male plakat, although they can be even fancier than the males sometimes!
I'm not sure from your discription, if you're sure she is not a veiltail, it is possible she could be one of the fan tail types like a half moon or something. It is also possible she could be a cross of two types which would be even more difficult to classify.
Yabbie and d_golem are good at this this type of thing, but without a picture it is tough. Maybe you could find a similar picture of a female betta online to compare her to?