Cult - glad you had "one of the best weekends in a while"

and the lines of communication are opening up.
About the episode this morning - her eating habits definitely would cause cognitive, motorskill, mood and behavior problems. Half a box of strawberries and a granola bar is not enough to sustain a a chipmunk in a day, let alone a person (even a tiny one). Eating and sleeping disorders can reak havoc on anyone, especially if they've been long-term. Mix this with diabetes and it's a recipe for a lot of problems, simply because diabetes requires a diet be followed and maintained including a specific amount of calory intake per day. Yes, losing weight and maintaining a healthy weight will help keep it under control, but it sounds like she's gone from simply dieting to eating disorder territory.
(eating disorder = a whole new world of underlying psychological issues that tie in with BPD).
If she's passing out, it's a symptom of larger problems. The body doesn't shut down like that unless there's a good reason. I wouldn't write it off as only dehydration - it could be the result of long-term starving, which can/will mess up all the organ functions.
Any chance of having her see a specialist in diet? eating disorders?