I don't think Mossberg makes a semi-auto .410 shotgun.
They do make a pump action .410 though.
While the first rule of a gun fight is to have a gun, the .410 is probably not what most people would consider the best defensive caliber of shotgun. That distinction would probably have to go to the 12 gauge.
There have been some self defense type loads come out lately for the .410, mostly due I would guess to the popularity of the Taurus Judge line of handguns. Maybe the overall worst part of the .410 would be paying the ridiculous price being asked for the shells.
If the women of the family was small in stature and strength, I think I would recommend one of the Mossberg pump action 505 youth guns in 20 gauge like their item number 57110 with the 20" barrel. See here http://www.mossberg.com/products/default.asp?id=22&display=specs
. With some light loads.
At least you could afford to buy shells to practice with and become intimately familiar with the gun.
Just my opinion for what its worth. But you sure need to get some good instruction too, about safe gun handling, and defense technique. Ask lots of questions and learn all you can.