Here's a breakdown:
* Y si: This is a common Spanish phrase that means "what if" or "and if".
* quien: This is the interrogative pronoun "who".
* fuera: This is the imperfect subjunctive of the verb "ser" (to be).
* ella: This is the pronoun "she".
The phrase is used to introduce a hypothetical situation where someone is imagining what would happen if a particular person were involved. It often implies doubt or speculation.
For example:
* Y si quien fuera ella la que te ayudó?: What if it were her who helped you?
* Y si quien fuera ella la que te dijo eso?: What if it were her who told you that?
The phrase can also be used to express surprise or disbelief, suggesting that the speaker finds the idea of "her" being involved unlikely.