If I discard 4 cards from Invert Timelines, does my Jinx Rebel get +4 Might?

No. Your Jinx, Rebel gets +1 Might, not +4.

Jinx's ability says "When you discard one or more cards" — this triggers once per discard event, not once per card. Invert Timelines instructs you to "discard your hand" as a single instruction, meaning all cards leave your hand simultaneously in one event. So it triggers Jinx exactly once, giving her +1 Might and readying her once. (FAQ #1411 confirms each separate discard trigger activates her separately — but Invert Timelines is one trigger, not four.)

Compare with a scenario like three Super Mega Death Rockets resolving individually on the chain (FAQ #6974): each one creates a separate discard event, so Jinx would trigger three times there. Invert Timelines is a single mass discard, not three separate ones.