We had a good laugh today when she said, "The metronome messes me up."
This may sound like a remedial exercise, and I know for certain that my student doesn't enjoy this, but it's absolutely essential to develop a sense of rhythm and time. It's the only way you're going to play well with others. Even if you're a soloist, you're going to need to keep a steady beat, otherwise people will find it challenging to listen to you.
Whether you want to be a killer lead player or a rock solid rhythm player, practicing with a metronome is the most efficient way to improve your technique. Once you are able to maintain a steady beat and stay in sync with the metronome, you can make friends with difficult lines or chord changes more easily. First, you start the metronome at a tempo at which it is nearly impossible to make a mistake. It may be an excruciatingly slow tempo, but that's okay. You want to start super slow, so that you are properly training your muscle memory. Get it right in slow motion, and you can then incrementally get it right at speed. Just start at a nice, easy tempo. Practice a problem area until you can play it correctly. Increase the metronome speed by 5 clicks and repeat the process. You will eventually run into a speed at which your technique finally breaks down. Remember the top speed at which you could play with control. The next time you practice that spot, start 10-20 clicks slower than your top speed and build from there. It won't be long before you can sail through that lick or those tricky chord changes.
My student has told me that she has no rhythm. I beg to differ. She has an undeveloped sense of rhythm, but it's in her. All she needs is a metronome and a few minutes a day focusing specifically on tempo.