I hope this link to a
Google Earth view of Green Valley park works. The park is within walking distance of I-17 and seems to be in an industrial area with quite a bit of heavy truck traffic. I wonder whether she was a passenger in a big rig? Imo, her clothing fits with someone riding around in a cold, small, air conditioned space. It might explain the long-sleeved sweater dress layered atop shorts and shirt while (possibly) not wearing shoes. I highly doubt a sweater dress was necessary to sit at the park. After all, it was July in Tucson, Arizona.
Like you
@Bit of hope, I wish we knew more about her cause of death and time of discovery. I hate letting my mind wander, but there are a few scenarios that could explain how she got there and why.

I noticed a couple of places along the street around the park where, with the help of a 18-wheeler's size, a body dump could possibly go undetected depending on the time of day or night she arrived at the park.
I looked again for possible matches but had no luck finding any.