What's the difference between these two sentences

The verbal form "were" is a subjunctive in the present grammatical context; essential explantions can be found in the pdf "englishsubjunctive.pdf".

ii. Hypothetical subjunctive
This usage of the subjunctive is called for whenever the situation described by the verb is ‘hypothetical,’ whether wished for, feared, or suggested; the common thread is that the situation is not the current state of affairs. This subjunctive can occur with or without a word like "if" or "whether" that specifically marks a phrase as hypothetical. When if is omitted, an inverted syntax is usually used:

• Were I the President...
• If I were the king of the world...
• Be he alive or be he dead...
• If I were the President...

In most varieties of English, this subjunctive can be replaced by an indicative when the if-form is used:

• If I was the President ...
• If he was a ghost...

Another use of the hypothetical subjunctive occurs with the verb wish – I wish I were a bird; Joseph wishes he were a cowboy. This too is often replaced with the unmarked form. I wish I was a bird expresses exactly the same meaning, but technically "was" is not a subjunctive form. Some use the marked form even in the absence of a hypothetical situation – Johnny asked me if I were afraid – simply as a conditioned variant that follows "if" and similar words. This is commonly considered a hypercorrection.

What is to be particularly heeded in this explanation is the sentence "the common thread is that the situation is not the current state of affairs.". This means that is understated in the sentence "if she were to … train." that she is not actually going to leave earlier.
The form using the indicative, equivalent as far as it carries the idea of a hypothetical situation, is somewhat different inasmuch as it does not understate that her leaving was not planned to be earlier; her actual plan might be after all be to leave earlier.