Learn Hardcore Hindi: मैं आग से बच गई।

Because the verb here is बचना / बच जाना, which is intransitive: the subject is the one who escapes or survives, and there is no direct object being acted on.

In standard Hindi, ने is typically used with many perfective transitive verbs, but not with a sentence like this one.

So:

मैं आग से बच गई। = I escaped the fire / I was saved from the fire.
Not मैंने आग से बच गई।

Why is से used after आग?

Here से means from.

With the verb बचना (to escape, to be saved from, to avoid), Hindi usually marks the danger or source with से:

आग से = from the fire
खतरे se = from danger
मुसीबत से = from trouble

So आग से बच गई literally means escaped from the fire or was saved from the fire.

What exactly does बच गई mean?

बच गई is a very common Hindi way to say escaped, survived, or was saved.

It is built from: