I think you would advise against aiming for a specific pull but I heard she's a true killer machine lol.
I think aiming for specific trust rewards when there's a rate-up for those would be the best way to spend your lapis/tickets. Zidane specifically.
Obviously it's smart to have some stocked up lapis for when characters like Lightning pop up, but I wouldn't count on getting her even if I drop 30k lapis on pulls. It's not a very reliable plan.