First of all, congratulations. She is willing to go to the gym with you. You are a small step to success. There are many people with good bodies in the gym, so you need to show what others don't have in the gym. Basically, you have two choices. One is to train with her, run with her, and step on the elliptical machine together. Take good care of her in the process and let her feel your sincerity. The second is to do strength training, barbell, push and squat by yourself. In this process, don't relax, don't shout tired, let her feel your persistence and your man side. Which is suitable for you should ask the Lord for his own consideration. I wish you success!