When you're sharing an AirTag, it's true that the tracking behavior isn't quite the same as if you were the sole owner. Apple recently added the ability to share AirTags (as of iOS 17.0 and later), but there are a few limitations and quirks that can affect how real-time the tracking appears for everyone involved.
First, only one person at a time (usually the owner or the most recently paired iPhone near it) will be able to consistently get the freshest location data. This happens because AirTags don't use GPS directly—they rely on nearby Apple devices to update their location. So, when your wife is traveling with the AirTag, her iPhone is constantly pinging its location to the Find My network. That update will always appear freshest on her Find My app. For you, as someone sharing access, it can sometimes take longer to reflect new location info—especially if the tag hasn't recently passed by a new Apple device not associated with her.
Since she has an iPhone, wouldn't it be easier to just have her share her location via her phone, which uses GPS and is far more accurate in providing real-time location updates?