The exact origin of Allison's superhuman abilities is a bit murky, even to her. So far as she can tell, she simply had an intensive growth spurt in her early college years; she assumes it was some random mutation. What has been more important to her life is what she's done with them.
Allison had always been something of a fitness buff, and unlike many who aquire great abilities she didn't feel an overwhelming urge to grab a set of tights and punch crime. Even so, she wanted to do *something* positive... so she started a gym in Metropolis aimed at the metahuman population. After all, exercise equipment built to handle those of superhuman physical ability is very expensive and only independently wealthy or well-supported heroes can easily afford such. By purchasing some and charging a slightly more than modest membership fee, Allison hoped to bring the ability to fully develop heroic potential to the regular folk who got hit by cosmic rays or glowing goo or nanorobots.
It says something about the state of the world that Allison has been very successful, although she's not wealthy. The "baseline" section of the club is what actually keeps the place afloat (as starry-eyed hero watchers wait to catch a glimpse of a favorite figure, or perhaps hope something will rub off) but a number of street level and 'local' heroes are members, even a few slightly bigger names.
Allison uses this access to the metahuman 'community' to keep tabs on rumors and scuttlebutt, occasionally quietly offering a little help in the form of 'muscle' to a few up-and-comers, and also keeps an eye on few supercrooks who have registered as members under false names and aren't nearly as good at disguise as they think. She reasons that if they behave, hopefully it all means they might be going straight. And if not, then keeping them around and engaging them in csual conversation might allow her to tip off one of the pros, one day.
(On a final note, despite its appropriateness, 'Stonebender' is not an assumed name - Allison believes it's an old family name with roots in Ireland, although it's been quite a few generations since the family came over.)
Allison has always been an outgoing, extroverted 'cheerleader' sort. Becoming strong and resilent enough that she rarely has a problem with conflict has exaggerated this for both good and bad. She treats just about *everyone* as a potential friend, but she's got the overconfidence of a big fish in a small pond. While she is fairly potent physically, not engaging in world-saving shenanigans on a regular basis means she never really finds herself over her head, which means she almost never recognizes it when she IS.
While it's not quite arrogance, she also has a bit of well-intentioned bully in her. She always believes she knows better even when she really shouldn't, and thus is liable to push someone into a situation they'd really prefer to not be in in the belief that it'll be character-building. The natural exception to this is in her line of work, curiously enough, where she's very careful to not put someone on an exercise scheme too intense for their powers or development to handle. She just doesn't have much of a sense of perspective outside that domain.