Some dogs are just like that, eat one day, skip a few and eat again. I find smaller portions than you would normally feed help them eat a bit more often ( not necessarily each mealtime ) whereas a large meal puts them off for a few days. There is a new paste on the Market for dogs off the feed. It is by Arden Grange. Never used it but heard very good reports.
Obi the GSD is very fussy and skips meals, he is VERy lean because of it but very healthy so I don't worry now he is fully grown, I do put a spoonful or two of 'natures diet' in which he is more eager with than just dry food but still misses the odd meal.
As to your question, no, tripe is not balanced and she is likely to suffer poor health at some stage if that is all she eats.
HTH