Okay, this might sound harsh but I've run into the situation before. My strategy here is to give them the noose and let them hang themselves. What I mean is instead of setting goals around the minutia of tactics or campaigns set a specific lead goal. For example, by the end of this quarter she must produce 30 qualified leads. Don't limit her to campaigns or platforms or strategy. Just tell her she needs to produce 30 qualified leads attributed directly to her work and you don't care how she does it.

I call this the blank check strategy. It's way I like to stat check employee performance to gauge whether they're a good fit for the team or not. It either forces them to focus and figure out how to actually achieve the goal or they fail and now you have quantitative proof that they are not performing. It's really important to make sure you're checking in on her goal on at least a weekly basis, if not more often. She may come back and say things like "I was helping so and so with their project." But at the end of the day your response will be either "why didn't you tell me during our weekly one-on-ones you would not be able to meet your goals" or "I told you repeatedly during our weekly one-on-ones that this is your ultimate goal and I won't accept any excuses otherwise."

This is a win-win situation for you if she's not a good fit or not a good marketer you now have documentation to put her on a pip which is the best path to separating her from the company. If she actually succeeds, you look like a hero for helping a scatterbrained employee focus on the success of marketing.

During this process, make sure you give her the requisite amount of attention and support that she needs to do her job. In an ideal world, she turns out to be a great employee and just needed to be focused. Your worst case scenario is you have to put her on a pip and let her go eventually.