How far is too far for "relationships" for officers and enlisted?

I am a personal trainer and one of my clients is a Major. I am already uncomfortable with this because the only type of officer I, as a chaplain assistant, have this much contact with is an actual chaplain but even in this situation we maintain professionalism. She has been my client for almost 3 years now. She has offered me advice and have tried to guide me in many different directions as a soldier, so she is a great officer. Hands down one of the Army's finest srationed at the the Pentagon.

She has a 5 year old, as well as I, and asked if my son could come over and play with her son. I was hesitant but I allowed him. Is this too close of a relationship and or too close to a friendship for an officer and enlisted personnel to have? I want to remain professional on all levels at all times and make sure that I am not overstepping any boundaries. I don't fall under her command at all either.