I see 1000% where you’re coming from with Monica not being maternal however I think it’s important to remember that many of the kids in her team have little to no relationship with their mums and so any kind of positive attention from someone of their mothers age is more than likely to create that motherly feeling for the kids for example La Darius, it may possibly be that the feelings are all one sided (on the kids side).
I had a very very turbulent relationship with my own mother (and father) I was always looking for a motherly figure be that a teacher or a sports coach, I had my own daughter at 16 and still continually searched for a mum. In one particular job (I was 20 at the time) we had mentors, my mentor was exactly like Monica, very tough love approach and always wanted me to perform to the upmost of my abilities in my job. I found myself continually wanting to impress her much like these kids do for Monica. She took me under her wing though and I will still always think of her as a mum in many ways.
I also think they don’t show a lot, I was surprised to hear that she paid La Darius’ dorm deposits and had him for thanks giving! However ultimately I have to agree that once the kids leave Navarro and can no longer compete at Daytona for the win, she will lack interest in them.