It's stilted. I mean, you could contrive a situation where you wanted to put particular stress on ‘enough’ so that your translation would be acceptable, but you'd have to really try. Normally, negation in English is achieved by attaching ‘not’ to the verb (+ do-support when necessary, including here, yielding ‘she doesn't eat enough’).
It's hard to answer this question comprehensively (the position of ‘nicht’ in a sentence is known to give a headache to many a learner), but the easiest way to understand this would be that ‘genug’ is what is being negated here (she does eat, just not enough), while placing ‘nicht’ at the end of the sentence would negate the verb.
You can't fix it like that. The only thing completely fixed is that the conjugated verb comes second (in statements; things are different in questions and orders).
The first position can be taken by nearly anything yoiu want to emphasize. Usually you find the subject here, but this is not mandatory.
"nicht" is an adverb, too. The rules for adverbs are rather complex. Usually they are placed at the end of tghe "mid-field". Usually this is the end of the sentence, but tghere are some elements (like infinitives, participles, predicative complements and second parts of separable verbs.
You did niot mention objects. Usually they come after the verb, but, as already said, you can emphasize one of them by putting it first.
Adjectives are not elements of their own. As an attribute they are part of subjects and objects. As such they stand in front of the noun they qualify ("the blue house" = "das blaue Haus"). When they form a predicative complement, they appear in the end of the sentence (The house is not blue" = "Das Haus ist nicht blau").