The fluid most likely comes from the Skene's glands. There has been some research in this area, enough to suggest that female ejaculation is real, but obviously not enough, since some still insist it's just pee. As many will tell you from experience, if you encounter a true female ejaculation up close in person, you will know it is definitely not urine.
Of course, it is possible that some women do indeed urinate when they orgasm. Some working girls may even advertise that they ejaculate, drink lots of water before sexual activity, and instead, urinate.