Yes, it is a figurative way of measuring how to make a comparison between two people. For example on the level of intelligence he may have an IQ of 105 and she has one of 130. In an argument level one may be a bully and the other meek. In your sentences, maybe her cooking was lousy when they were married. She might have improved on that level.
I think it only has a figurative meaning: there's no suggestion that you get on better with people on the first floor than you do at ground level.
For me it means in different ways. We get on with people at many levels: at work, in shared interests, emotionally, sexually, intellectually, sharing a sense of humour. It's this sort of thing to which the writer must be referring.