I have a 30g sorority with seven girls in it, and as many plants as I can physically get in there and still see my fish... ;) (I've probably gone overboard) And sometimes mine still get tail bites. But, I totally agree with what Vegas and Little have said, more room, more girls, and as many places to hide (and at all levels of the tank, top, middle, and bottom) as you can cram in there.
My guys all typically grew their tail notches back in about two weeks, maybe as long as a month? since the girl's tails are so much shorter, they grow back in pretty quickly as compared with the males. :)
I've read that high-protein frozen food helps.
Also, one more suggestion, you may want to get at least five girls...you may want to get a couple of extras. Two of mine were healthy until they went into the sorority (30g, LOTS of plants), but they couldn't handle the stress and died a few days later despite having been pulled out within the hour. I started with nine, but I'm at seven now, with another in QT until she can grow a little more. Now, mine are also coming from Petco and Petsmart, so their health, even with a 2 week quarantine, is probably not the best anyway. This may not be so likely with breeder fish or fish from a more reputable source.
I'm sorry about your girl, but I'm glad you were able to save her, and hopefully things will go more smoothly for you in the future. :)