I worked for this company last year on a project and got hired on again for another project this year. My position this year carries a great deal more responsibility, and I'm being paid accordingly. They also hired back a girl I worked with last year who, in my opinion, did questionable work even back then when we were doing very simple and mundane tasks. I was pretty surprised and a bit apprehensive about working with her again on a much more involved project, but I gave her the benefit of doubt and tried to be optimistic. However, it's been several months, and she's just not cutting it. The quality of her work is poor, and I'm constantly having to correct her work. I am not her superior, but we both work on the same stuff, and our supervisor is off site and never really sees what's going on on-site. I've now had to point out this girl's mistakes numerous times and have had to write her fairly lengthy emails about things (our work schedules rarely overlap as I work on her days off and she works on mine). I have tried to be as polite and subtle yet clear about things as possible, but she's still starting to get an attitude and has now started to argue with me about a few things. It's compromising the quality of our work and content, work and content that has my name on it, and I'm not okay with that. I am considering having a conversation with our supervisor about it, but I'm conflicted since my coworker is actually a personal friend of mine and not someone I want to cause problems for. She's just not doing her job and doesn't seem to care.
What are your thoughts on this? Ever been in a similar situation? What should I do?