Current coworker as a reference if work doesn't know I'm looking for a new job?

It sounds a little odd, I know. I need a third reference as I apply to new jobs, and I don't have enough experience to fill that out based on past work. I have a good relationship with a coworker personally, and we work together quite a lot so she knows my quality of work. And while she doesn't know that I'm currently looking for something new, we've had a couple conversations in the past from which one might gather that impression eventually.

So, I don't think if I asked her to do it, that she would inform my supervisors. But would asking her put her in a difficult position? Does putting a current coworker down in a situation like this look odd to an employer? Does anyone have experience doing this sort of thing?

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