The first time (!) I transitioned, I felt major flu-like symptoms including achy muscles. Also, because I went from regular coffee to decaf (cold-turkey), all my little caffeine-related aches and pains screamed for more caffeine until they were flushed away - joints and tendon-like places.

I would guess that you're experiencing some sort of withdrawal from some food or chemical that was a regular part of both your diets. If you experienced the same pain and it went away, it's likely that hers will too.

That said, I hope that someone with more medical knowledge answers this question!

P.S. This might be a good question to ask Robb Wolf.

It's just a coincidence. Look elsewhere for the cause.

This could be indicative of an electrolyte imbalance as this sounds like musculoskeletal cramping. She may be mobilizing water and losing sodium and potassium along with it. I would suggest increasing water intake and keeping a food log (such as Fitday or Nutrition Data) for a few weeks/until eating patterns are well established. Compensating for electrolyte losses is important. It might also help to include offal and higher sodium/potassium foods in the diet in the short term.

I had similar symptoms my first couple weeks. When I started supplementing with potassium and magnesium and extra salt I felt better and those symptoms went away.