For a long time, I was the only (or one of a couple) females in my dojo. I never had an issue being the only one. I actually embraced it. I loved rolling around with the guys and I took advantage of having the changing room all to myself. In fact, when other females did come, I was a bit pouty because I had to remember how to share.
Most people in my dojo were either 1st kyu or above or near beginners like me, so the rank issue never really came into play. Sensei was using me for ukemi after training a few months (previously took aikijitsu for 8 years) and that may have made a difference. A lot of guys loved to really toss me about because they knew I could take care of myself. If someone was being too gentle, sensei would tell them I could take care of myself and not to worry. Maybe broaching ukemi with your sensei wouldn't be a bad thing.... just depends on their personality and how receptive they are to feedback. Best of luck.