As Luck said it is random when she visits. Please see below for the news text!

"If you’re lucky enough to get a visit from sweet Tempest via random event, you might just get this shocking new HA border. You will not get this stormy border from summoning everyone’s good friend Tempest with the Tempest Lightning Rod. It’s only achievable randomly through visiting her by random event."

Not a problem but yes it is completely random when she visits. Sorry!!! I hope you get it soon!