does diana lunari effect still trigger if you gust her?

Yes — if the showdown has already begun, Gusting Diana doesn't stop her ability. Once her "When a showdown begins here" trigger is on the chain, it resolves independently of its source, so she doesn't need to stay on the board (FAQ #10222).

Sequence: the showdown begins and her ability goes on the chain → your opponent plays Gust in response, returning her to hand → Gust resolves → her trigger resolves, letting you pay [1] to Predict and draw a spell if the top card is one. One note: the [1] payment is optional even if you have the energy floating (Vendetta rules update), and since her text doesn't require her to be present, the whole effect executes normally from hand.