Can you react to Empower? So if Kayle gets empowered, can I react with Starcrossed before she gets Deflect?

Yes, you can react to the Empower activation with Star-Crossed before Kayle gets Deflect.

Here's the timing: Empower is an activated ability — it goes on the Chain as a Pending Item, creating a Closed State (Rules 377.3, 827). Star-Crossed has [Reaction], so you can play it during that Closed State. The ability hasn't resolved yet, so Kayle is not yet Empowered and does not have Deflect 3 — you can target her freely.

Sequence:

1. Opponent activates Empower [3] on Kayle → it goes on the Chain as a Pending item.
2. You play Star-Crossed (Reaction) on top of it, targeting Kayle (enemy) and a friendly unit.
3. Star-Crossed resolves first (LIFO) → Kayle returns to hand.
4. Empower resolves → Kayle is no longer on the board, so the Empower action does nothing.

The Empowered dependent keyword (Rule 828) only becomes active after the Empower action completes — that's the whole point of reacting before it resolves.

Note: You do need a second friendly unit on the board to target for Star-Crossed (it requires both a friendly and an enemy target).