I think she just didn't know how to properly fit her friend and wanted to help her dress well. And I assume was short of cash or beleived the clothes would be expensive.

It was pretty ridiculous, but I'm guessing it's something someone not on the internet might do due to lack of ability to find information. When someone does something like this out of the ordinary, I'd just assume they're wacky and leave it there. She must have been petrified to pick something out for her friend and to make a mistake more so than asking a random stranger to cover her on it. Wow!