Estrellita Mercado is a remarkable young woman that put herself through medical school in order to get herself out of the aging Washington D.C. neighborhood she grew up in. Of course, she also wanted to help people, so that was another motivating factor for her going through medical school. Over time, she found her calling: the field of physical therapy.
Lita worked in this field for a couple of years when, for the first time, she met Keith and Teddy Remsen. They'd been caught in a bomb blast, and then hospitalized for months while they were patched back together by various doctors. Lita was working with Terry as the White Event occurred, a mysterious phenomenon that woke Keith from his coma, and (as they found out) gave him amazing powers.
When Doctor Ballad decided to found a Dream Institute in order to help Keith use his dream powers in a responsible and professional manner, Lita readily signed on in order to keep the Remsen kids in order (and in shape). She filled this role during the entire time the Institute was operational; it was open for over a year, until after the Pitt incident.
When this horrible thing happened, Teddy was thrown into a coma, and Keith got a bit... unstable. Furthermore, Keith got Drafted by the Army, and, without either of the paranormals handy, the Institute didn't really have any more reason to exist. As such, Doctor Ballad closed the place down, and volunteered to help the Army in its work with paranormals, since he'd been studying one for some time.
This, of course, allowed Ballad to take Teddy with him, since she was a paranormal, too. Lita, knowing where she was needed, also went with Doctor Ballad, serving to help rehabilitate paranormal draft-dodgers who were injured in their attempts to escape the Army. She fulfilled this function until after the War, when the Draft was no longer needed.
By this time, Keith had managed to get Teddy out of her coma, though he himself soon fell into one (after the events he survived in the War), retreating from the real world in order to play his days out in the dreams of others. He finally recovered from this state, though, and (having been bed-ridden for years), needed a physical therapist to get himself back in working order again.
Since Keith always liked Lita, of course, she'd be a likely candidate for such work. Especially since, with him and Teddy being once again aware of the outside world, the Ballad Dream Institute could once again open its doors...