How can a girl with a 7th grade education get her GED or HS Diploma?

There are several serious challenges here. The two primary ones are this girl's depression problem, and her inability to drive. She's getting kicked out of school for a reason, and whether it is related to her depression or some other issue, she's making problems for herself. Getting help for a medical condition (which is what clinical depression is) is completely her responsibility. You can offer to take her to a clinic or help her get in touch with the local public health authorities, but she must be willing to get her situation analyzed and dealt with. As far as transportation is concerned, neither you nor she can do magic. In order to pass a GED, since she has only a 7th grade education, she probably will need to attend GED preparation classes, which means locating one which is near public transportation, getting help with driving her through a community service organization (a church? a volunteer group?) or finding some other way to get her there. Is there a community college in the area? (Some offer GED classes.) Could student volunteers from the college take her, or could she ride with students who go back and forth regularly? Her two basic challenges must be resolved before anything else can be done for her. (And, by the way, she's awfully lucky to have someone in her life like you who cares enough about her to try to help her out.)