<human>: Hello relationships! This is a work issue, so I appreciate any professional perspective! 

I've been working for a software company with extremely complex products, and I took it upon myself to be a trainer for the most difficult product we provide. This means I travel all over the USA to help new users understand our software so they can use it efficiently. I'm passionate about this product, and have been loving learning more about it and helping our clients to succeed with it. On our current training team I am the most senior member so this project is entirely on me -  my boss will not allow our other trainers to participate. I don't mind it at all; the client in question loves me and has bought training from me specifically in 5 different cities. I enjoy working with them and their users. 

The problem lies in our client's training manager (32F). She travels to all the sites, despite not having experience in the industry or our software. She is close to my age and female so I understand the struggle she faces quite intimately. 

In a nutshell, she has been sending nasty emails to my company questioning my competence. In my role, I must be an expert on our software and provide answers to questions from new users, even if I don't know the answer off hand. If I don't know the answer on the spot, I  do the appropriate research and follow up with those curious. This
individual I will call Steph, has been sending emails to her superiors and my company complaining that i don't answer all questions on the spot. 

My company has since told Steph she was out of line, but I must face her in 5 cities this month for my training. I want our relationship to be good. Should I invite her for lunch and try to get her to understand that the complexity of this industry means I have to do research here and there? And connect with her on some level? I don't want to have bad blood with a woman I will have to see several times this month, and I want our
 companies to work in harmony. I'm not sure how to make this right... But I want to make things right between our firms. How do I go about this professionally and effectively?

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: My client questions my competence despite not knowing the product I train. How can I get on good terms with her and make her understand so we can work together?