Let's let everyone know what Morton's Neuroma (MN) is: a neuroma is a nerve that has been pinched or otherwise irritated enough that it becomes inflamed and scar tissue builds up around it, causing chronic irritation and pain. Morton's neuroma always occurs between the third and fourth toe. It can often be caused by flat feet or poor shoes (pinching the toes together), but there are many possible causes and many other conditions that present similar symptoms. In really bad cases, the nerve needs to be deadened or removed surgically.
Can yoga help? Possibly. You were right of course to suggest your student see her health care providers, but there are a few poses that could be very good for her. Since one potential cause of MN is flat feet, Saddle pose could indeed be a great pose for her. Also the Ankle Stretch
http://www.yinyoga.com/ys2_2.0_asanas_ankle_stretch.php pose and Toe Squats
http://www.yinyoga.com/ys2_2.0_asanas_toe_squat.php could be helpful.
Another thing your student could try is the Zipper: this is a delicious way to open the toes. There is an old Daoist saying that a man with open toes has an open mind, and I am pretty sure this applies to women too! To do the Zipper, take off your shoes and socks, bring the soles of your feet together and interlace your toes. Let your toes marinate for ~ 5 minutes. Juicy! I sometimes ask students to do this while they are waiting for the yoga class to begin. If a student can't interlace (zip) the toes, that is not a good sign! They need to do this more. If she really can't zip up the toes, then tell her to just use her fingers to spread the toes. Eventually, she should be able to do this without any hands! That is really impressive and you can be the life of any party if you show people how to do the zipper with no hands.
Saddle, Toe Squat, Ankle Stretch and the Zipper may all be useful yin poses for someone with Morton's Neuroma.
Cheers
Bernie