Since it's not a prop you'll have to make it into one before you can save it as such. The easiest way is to select it and open up the grouping tool, add all the material of bra to a new group and then spawn prop or create new prop. Parent this if you want it saved as a smart prop. Now if you open up a prop directory you will be able to add your new prop. Keep in mind though that to use it will take quite a lot of scaling as it is made for Jungle Babe's unique built!