Trailers are harder work. But do you have panniers and a rack? If not then why buy them when the trailer will all ready do the job, even if it is slightly harder work. Can you fit pannier to the wife’s bike?
Panniers need more careful packing to balance the load and to fit everything in, while the trailer is easier and quicker to load as its usually the one bag. But you can easily overload the traile.
Trailer can give more freedom as it can be unhitched quickly and then you can use the bike without any load should you want to. However the trailer can be a bit of a pain when storing the bike, they do take up a lot more room
Hope that is of some use.