One of the main issues is that personal training isn't a very regulated industry. Your trainer could have a college degree or a "home" degree. I'd ask for credentials next time.

Wow, I don't even let my mom get away with 'because I said so':) . You are not a child. You have the right to question anyone to gain clarity. Even more so if you happen to be paying that person for their expertise.
People answer with 'because I said so' when they don't know how to articulate an answer, don't know the answer, or have no respect for the asker.

You have done an amazing job, even more points for sitting through tense training sessions.
You are obligated only to yourself. If this chick isn't adding to your life-ditch her,and move on. Don't give her anymore thought then shes worth.
I don't think you are using this as an excuse to not go to the gym. I have no doubt that you'll continue with your workouts,whether its with a new trainer or on your own!