Let's leave out the fact that the owner is a 92 yr old widow on fixed income, that this is her only building and it represents more than half of her income...
I would have to investigate, but I've gotta believe this service is legal and code. Every year a (different) City Inspector walks through the building, and if the service wasn't legal surely this would have been brought to our attention by now.
The building was built in 1960, my Parents bought it in '66. It is next to a popular Catholic Church, and there are about 6 4plexes's on the block, with an equal number on the other side of the street. The area is surrounded by owner occupied single families. It sure looks like all of the 4plexes were built at the same time, they all look alike. It would not surprise me to find that many/most still have 60 amp/fuse service.
Now how would you approach a 92 yr old widow in declining health that she needs to spend 5k to replace something that isn't broken? Microwaves and window air conditioners have been around quite a while, and I truthfully can't remember the last time I've had to replace a blown fuse, in any season.
I appreciate some people's need to jump on the soapbox, pound their chest and say what they would do, and what others should do, but to me, it's idealism vs. realism. I doubt anyone here would badger their elderly Parent to spend 5k just because they have to move some fuses around once and a while.