Alright Richard, I may have been wrong about my purple guy being an herbivore. In spite of my fish guys four years in college studying biology or whatever he seems to have mislead me. This site:
www.advancedaquarist.com/issues/dec2004/invert.htmreferences my slug as Hypselodoris bullocki, apparently a highly specified predator with slim odds for survival in a tank without a very specific food source of sponges. Apparently in addition to that, nobody knows which sponges for sure. So he may not be a good choice for a reef tank if that's what she's running, and indeed may not even live.
Check out that site, and I believe he references some slug forums as well and see what might be best for her.
Meanwhile I'm off to go see what kind of slugs I CAN keep alive.
ETA: After finding out more about the species and what type of food it consumes I called the guy I bought it from to question him. According to many internet sites these slugs have a low survival rate and need a very specific diet of certain sponges. According to the guy I bought it from, he is aware of the special diet, and supposedly as long as you have LOTS of live rock in the aquarium that sponge variety is probably present and he is likely to find the source of food he needs.
I guess as far as these slugs are concerned "you spends your money and you takes your chances."
That said, I'll spend more time researching my next slug to be sure he is "easy" to care for. Apparently some slugs thrive on regular vegitable growth in the tank, same as a snail. If you're going to pick one up for mom, I suggest doing your research, seeing which variations eat algae/vegitation and are still interesting to look at, and obtaining that. Less chance of death, less chance of it harming her corals if she has any, and less chance of unduly tormenting something for no reason.
We'll see wha happens.