Perhaps you are suggesting that middle class females would remain in the labor force despite a UBI. I find that premise dubious: the feminization of jobs capable of paying a middle-class salary may be driving males away from such jobs, but work is work. Females are not inherently inclined to toil at "feminized" jobs they do not care for any more than men are intrinsically attracted to perform "masculine" work they despise.

But even if we were to assume the advent of a Calvinist work ethic among middle-class women, the average wage for those women would tend to fall to a level quite unlikely to maintain a middle class/poor distinction. Upon introduction of a UBI, middle class females would not feel pressured to accept anything but "meaningful" work. Such jobs are necessarily scarce. With demand for those jobs perpetually outstripping their supply, wages will have a tendency to fall to zero. Today's unpaid internships and clerkships, which are already puzzlingly popular among the upper middle class, are illustrative.

(http://www.autoadmit.com/thread.php?thread_id=3908820&forum_id=2#35633551)