Does she use the fan in her range hood? If not, she should.
We have a similar situation in our home. The offending detector isn't actually in the kitchen, but nearby. The only other possible location was around the corner on a living room wall, but the wife nixed that idea.
Besides location, there may be something else wrong if the detectors continue to alarm for an hour. Ours usually stop as soon as the Hush button is pushed. They also have a feature that when they aren't alarming, pushing the Hush button reduces the sensitivity of that one detector for a short period (30 minutes, I think) to prevent nuisance alarms while cooking.
Another thought: smoke detectors sometimes actually require cleaning to remove accumulations of dust, cobwebs, etc. Might pick up a can of compressed air like what's used for cleaning computers and give it a try.