Without a vent picture I can't identify the sex 100% but there are two physical characteristics that make me assume female.
1) Short tail trailers. Assuming that umbee is housed solo I would expect the trailers to be about half way past the tail. However some male umbees do have slow growing trailers so this is not an exact method of identification.
2) The black coloration on the pelvic fins. If an umbee has black coloration on its pelvic fin it always indicates a female umbee. I do not know of any male umbee that has developed black colors on its pelvic fin, but yours could be an exception.