After the election. Meaning that the governor gets to appoint a replacement until the next senatorial election nearly 2 years later.
The election is in November and I think the winner gets sworn in on January 2nd or shortly thereafter. Resignation “at the end of this year” I’m not sure what that means. The Gov can appoint someone for a couple of days? It’s weird she didn’t just say she is dropping her re-election campaign. She doesn’t need to resign apx 2 days before she gets replaced but there may be implications about procedural votes etc.
I would expect that she’ll serve out her term and be replaced by Gallego or Lake. Mark Kelly was reelected in 2022, so there won’t be an AZ Senate race in 2026.