I would totally make sure that there isn't something medical going on 1st (more than just a brief visit in the ped's office). My sister couldn't make it to the potty to pee but could do bm in there without issue. Everyone was frustrated and she was ashamed. At I think age 5 or so she finally had a scan of some sort and found out she had a tumor the size of a grapefruit very internally that was pressing on her bladder making her be unable to recognize when she needed to go.
If this has been ruled out, then I would keep her in panties and use the plastic training covers (to save the house and car!) and have her help to wash them everytime in the sink. I wouldn't be angry, disappointed or anything else negative...nor say a word to her about what she has done, other than the fact that the panties (and her) now need to be cleaned. This will be a pain, but it will be so to her as well and she will have to stop and clean up at very inconvenient times such as during a great tv show, while playing, etc.
I also think she has become too stressed now about peeing in the potty (for whatever reason...) and needs to settle and relax. If everyone is tense and uptight about her accidents, she will be slow to progress since she associates pee with tension/anxiety (no matter where it is). Read, tell stories or jokes, get a new coloring book(s) or reading books that are just for potty time (sitting on the potty) so she wil want to sit there just to use the cool new items! Keep positive, positive, positive!!!!
Best wishes to your friend!