I wouldn't start a sorority with one female and then add others in. It could be pretty risky. I'd only start with a bunch of girls already totally used to being together. I got all my girls from a petshop where all the females were in one tank, then travelled home in one bag.
As for the stress stripes, give her time. My girls have been home 11 days now and a few of them still show some faint stripes, even though they have gone from skinny, starving little waifs to chubby princesses! :p
If you would like some tank mates for her, I would get some pygmy cories. Cute, tiny, highly unlikely to bother your girl, too small to be seen as a threat (unless she is one of those psycho murderers) and would fill in the empty space. :) I just think adding in new girls would stress her out.
If you do try it, plant or decorate your tank as densely as possible and have backup tanks for all the girls.