But yesterday, with lunchtime queues lasting three and a half hours or more - some said they had waited up to six hours - Mary didn't even try.
"These last few days the Spanish Guardia Civil have been strengthened, so yesterday instead of nodding us regular pedestrians through as they usually do, they checked our passports, turning over page after page, and searched us to see if we were smuggling tobacco. It's a bother when you're with children. I'll have to go tomorrow for the weekend shopping. I'm dreading it."
Mary speaks in rapid Andaluz, punching the occasional English word - "shopping" - into the torrent of speech, like most Gibraltarians.
Her neighbour Tracy Spiteri was more forthright. "We feel besieged. What happened when the Algeciras fishermen blockaded the border last week was a siege, and in a late 20th-century Europe that's supposed to have open frontiers. And now Matutes threatens even more restrictions. He's gone berserk." She snorted in disgust.
Tracy's husband, Charlie, "did tobacco" in easier days when Gibraltarian authorities turned a blind eye to nightly trips by fast launches carrying crates of Winston cigarettes to deserted Spanish beaches. That stopped when the Foreign Office threatened direct rule on the colony unless Gibraltar cleaned up its act. The sight of black rubber fast dinghies bobbing in the marina, waiting for a smuggling run across the straits, is a distant memory. Even Madrid concedes that Gibraltar is no longer a red-hot conduit for drug or tobacco smuggling, despite the body searches inflicted upon Mary.
After the tobacco runs ended, Charlie was desperate for work, handing out leaflets for a restaurant to make ends meet for Tracy and their four children. She recalls Charlie's enforced idleness with bitterness. "You'd think that with the thousands of Spaniards who come every day to work on the Rock, they'd find a job for Charlie, who's Gibraltarian born and bred."
But now, she says, with evident pride, "he's got a stable job in the local dockyard. He's had it for six months now."
"Siege mentality" is no mere figure of speech in this British colony born as a fortress, where a joint French and Spanish siege in 1779 lasted two years and ended in Gibraltarian victory. Street names and pub boards are all that remain of Britain's military legacy since the MoD in recent years wound down its operations to almost nothing.
But old loyalties burn bright. Jane Howard, owner of the Cannon Bar, down crooked, cobbled Cannon Lane, said yesterday: "We talk of nothing else but border problems and our bitterness with Madrid, and everyone comes in here, from building workers to dentists.
"I've had customers this morning complaining they've been caught in a Catch 22, with this new passport ruling, because if you've got a Gibraltar- registered car, you have to carry a Gib passport to drive it.
"They're even stopping motorbikes now, poring over every piece of paper you offer them."
Christine Ryan, an Englishwoman who has lived on the rock for 12 years, came into the bar, having braved the border crossing to buy a piece of trimming for a cushion. "It's such a pain. Those queuing were mostly foreign or Spanish who'd got caught trying to go home. The atmosphere is the worst I've known it."
Andrew Hoare, whose family has run the sports shop in Main Street for three generations, has seen business drop this week. He sighed wearily. "We've been through this before under Franco. It's just another siege. My grandfather survived the war. My father survived the closure of the frontier, and I'm having to go through it all again. It turns us against Spain."