This is an excellent question Maya, and not one with a definitive yes-or-no answer. When it comes to socializing, horses are like peoplethey are individuals whose need for social interaction varies. Some become very stressed when they are not able to be with another horse, and some choose, on their own, to spend time away from the herd.
It sounds like your mare is able to have physical contact with the two other horses, and that it is a stable “herd.” The fact that the horses can touch and groom each other is important. The grooming and attention you are giving her 5-6 days a week is also helpful. I would just want to be sure that she is mentally enricheda rolling treat ball, a scratching board, and things for her to manipulate with her mouth will help decrease any boredom for her.