Check your passport after being stamped on entry to Spain.
Make sure after you have presented your UK passport to the Spanish border control, to be checked and stamped, that you check the date.
My friends who arrived back in Spain on the 4th of January 2022, had to use their passports at the Bank. At the Alicante airport when they arrived they went to different border control desks, one had their passport stamped 04/01/2022 but the other was stamped 04/01/2021!!!!! Obviously someone has made a grave mistake, so there must be others with an incorrect entry stamp.
Now she's going to have to prove she entered on the 4th of January 2022 not 2021, as otherwise she will have a big fine.
Its easy just to take your passport when its given back to you and put it in your bag without checking.