Poor girl is quite sick or she would be moving around and eating. Have to run out for the day, and I'm sure others will be along, but please get her indoors right away, in a quiet, safe, warm, comfortable place with food and water near her. Monitor, eating (or lack thereof), drinking (or lack thereof), pooping and other behavior closely. She can't afford to expend energy trying to keep warm. If there are any treats she especially likes, offer them. You may need to start giving her 3 drops Polyvisol liquid childern's vitamins daily (without the added iron), dribbled gently along her beak line with a dropper, so she doesn't choke. This is to try to maintain some semblence of vital nutrients.
Now, to figure out WHY she's sick. Not always easy (correction - not often easy!). When did this behavior begin? When is the last time you saw her eat well? Etc. Etc. Relay this info and anything else you think could provide clues........
JJ