When it comes to Lonnie Samson, Clara is truly the woman behind the man. If she hadn't caught up with Lonnie after his disastrous encounter with his lit professor and told him not to take it personally, it's quite likely that Lonnie would have gone to the administration building and quit his major—again. Something like that could have caused Pop to lose his temper and swing his ax for real this time. Therefore, Clara may have unknowingly saved innocent lives when she chased Lonnie down that day.
Fortunately, though, Clara not only talks Lonnie out of quitting his major, but becomes his primary source of support, his girlfriend, and later, though we don't see it happen, his fiancée. In other words, the feelings become totally mutual between these two.
Lonnie aside, though, there's another factor that drives Clara into their relationship: her own lackluster family situation. Having spent most of her life butting heads with her father, Clara can immediately relate to Lonnie when she hears him mutter during their English lecture, "You're no grandfather of mine" (9.9). In their shared pain of family members' rejection, Clara immediately connects with him even though they haven't spoken a word.
Like Lily, however, Clara's no saint. It's not that she doesn't have the right to be mad at her dad—after all, he's super hard on her and her mom. Still, getting to know Lonnie and his family situation helps her see that she is actually a huge part of the problem. Newly engaged to Lonnie and preparing to meet his family, she reflects on this:
Like a weird stranger walking through a door, an odd idea stole into Clara's mind. It was this: how […] Clara was… a bit of a bully, just like Dad. (37.6)
Clara doesn't only change Lonnie, then. She, through being in a committed relationship, learns to change her feelings toward her parents as well, as well as better understand her role in their dynamic.