I do not know what the Garmin transmitters do about reporting battery levels.
ALL the transmitters in the PPS/Shearwater family report battery level. I prefer the PPS version to the Shearwater "Swift" version, if only for the ease of battery change. It is unlikely you would need the fancy feature of the Swift (it listens to make sure it is not transmitting at the same time as another nearby transmitter), so long as you don't turn your gas on at the same time as your wife does. If this is a concern, get one or two Swifts. They are all about the same price, new, but you can find the PPS versions for around $200 used. Me? I'd get one Swift for your wife's rig, and a used PPS for my rig.