Both sentences are fine. Both are counterfactual conditional sentences, firmly anchored in the present (and future), and, therefore, in complete conformity with the "second conditional" referenced below. Also, each of the two sentences references, in the relative clause, an imaginary condition or event that is (or would have been) in the past relative to the present time of the main conditional sentence.
The wikipedia entry for "conditional sentence" identifies 5 types of English conditional sentences. In the wikipedia taxonomy, both of the sentences in question are examples of “second conditional”, “…the pattern where the condition clause is in the past tense, and the consequence in conditional mood (using would or, in the first person and rarely, should).” The entry proceeds to observe, “This is used for hypothetical, counterfactual situations in a present or future time frame.”
The specific meaning of the condition clause, "If I could go back in time", offers opportunities for confusion about the time setting of the consequence clause. This is a result of the fact that the conditional clause references a "past" in a way that analogous "second conditionals" (as, "If I could fly...") do not. (My initial response to the question took full advantage of those opportunities.) On closer examination, however, the consequence clause reveals itself to be likewise firmly anchored in the present (or future).
The present tense in the relative clause of the first sentence is the historical present, used for historical or fictional narratives and therefore either in the past or fictional. The second sentence uses the simple past tense. Perhaps there is a subtle difference between "she never leaves" and "she never left", but the meanings are very close if not completely convergent. The question, as posed, seems to imply that the first sentence is obviously correct, but wonders whether the second is not suspect. Because of its use of the historical present, the first sentence would seem to be, in fact, the less colloquial of the two variants.