No covid controls, no plf forms at the border or anything else. You just show your passport to the Spanish (if she is a UK passport holder then make sure the Spanish stamp her passport out - you need to ask), and then again to the Gib passport officer. I was there in September, crossing the border on foot twice a day for a week, and never had to wait more than 5 minutes. It’s completely straightforward and I wouldn’t worry about it at all. Covid hasn’t changed anything - the only change is the need to get passport stamped (Brrr Brexit…).