My sister in law is a TA and I always book trips with her too. She's in a city where most of our guests don't live either. I think it'd be really offensive to her if we didn't use her. It'll be a lot of work but that's her business and I want to support her job, especially since she always books my trips and finds me the cheapest deal. People can book through email, and this day in age, most people are use to doing that. I don't think it's worth risking the relationship with your aunt. Maybe you can just explain to her in advance what you expect and maybe even ask her if she wants to do. Going to her first gives her the option of backing out, but also shows that you respect and trust her.
Good luck!