Even though the answer chosen as the best answer covered most of the requirements for treating insomnia using the paleo paradigm, I have a few recommendations to add based on my extensive research on insomnia as a result of suffering from it myself for many years.
Whenever anyone has insomnia for unknown reasons when they are living a generally healthy lifestyle like your gf is, I suspect cortisol dysregulation (or adrenal fatigue if cortisol dysregulation has lasted a long time) before anything else. Adrenal fatigue is a much more common problem than both the allopathic medical community and the paleo community recognize (although some in the paleo community give it due attention). Although I don't see any obvious behaviors in your description of your gf's lifestyle that would contribute to adrenal fatigue, you mentioned that her sleep improved after she removed caffeine from her diet, so if she was consuming large amounts of caffeine every day, or even moderate amounts later in the day, that alone could have caused elevated nighttime cortisol that could take several weeks to undo, even after removing caffeine from the diet.
Fortunately, it is actually easier to diagnose adrenal fatigue using tests one can do at home for free or salivary tests that one can order online and do at home then send to a lab than it is for an allopathic doctor to make the diagnosis. This article is the most comprehensive and useful I have found on how to diagnose this condition: http://www.stopthethyroidmadness.com/adrenal-info/#
If money isn't an issue for you, I would order the 24 hour salivary cortisol and DHEA tests, or at least the cortisol test from the lab listed on the above web page. If you want to save money, the 4 tests and questionnaire on the above page are often adequate for diagnosing adrenal fatigue. I have found the daily body temperature recordings to be especially helpful for myself (see my question here: http://paleohacks.com/questions/74722/is-body-temperature-an-accurate-indicator-of-metabolic-function-dysfunction). Adrenal fatigue is relatively simple to treat, and your gf doesn't seem to have symptoms of more advanced adrenal fatigue like inability to rise from bed in the morning or extreme fatigue, so if she does have an imbalance in cortisol it should not take very long to correct.
It is also worth playing around with macronutrient ratio and meal timing/frequency, as these factors can contribute to insomnia in various ways also. Eating too late can cause insomnia for some people, as the best answer described. On the leangains website I just read that carbs promote water retention, while protein promotes diuresis, so it might be worthwhile to increase her carb intake if she is low carb or especially if she is very low carb, at least on days including intense exercise, as explained in the leangains approach. Just one of many possible explanations for why she has to urinate multiple times per night.
Lastly, I would try supplementing with either 5-htp or tryptophan to increase serotonin and melatonin levels before going to bed, as my sleep quality improved drastically when I increased my dosage of 5-htp from 100 to 200 mg before bed time. Supplements that increase GABA levels like L-theanine and valerian root are also worth experimenting with, since GABA deficiency causes insomnia.
Of course there are many other potential causes of her insomnia which other people have already covered, but I felt obligated to add cortisol dysregulation to the list because it was barely mentioned so far (props to White Dolemite for mentioning it). In summary, I recommend getting as many lab tests done as you can afford or feel appropriate, as well as the free tests I mentioned above that you do at home, and just keep experimenting with behavior and/or supplement modifications until you find what works.
