What she has with Boimler just doesn't feel like a friendship. You need camaraderie to mitigate Mariner's off-putting cockiness
Which they have. She looks out for him, he looks out for her. Whilst taking the piss out of each other or occasionally shooting each other with phasers.
If she WERE a man, that would be the standard "bro" relationship guys have.
You seem more exorcised upthread that they aren't into each other sexually. So I don't buy that your concern is they don't seem like "friends".