Riding coat question?

I've competed at hunter jumper for years and always bought Dover jackets... I had a friend who is new to showing and she asked me if she could use a black suit jacket for shows. It almost if not identical to my show jacket if darted in on the sides. I never thought of a suit jacket because I took the plunge and bought a hunter/jumper jacket for showing. What do you guys think? She is going to compete in IHSA as well as open shows.