@Joseph79
As a (relatively) new host who favors long-term guests, I'm not getting a good feeling from what you've mentioned about your potential guest. It feels like your potential guest is haggling, and I really hate hagglers because they are NEVER worth it.
Why is the guest asking you (host) about Airbnb's guest service fees? Hosts have no say or power over the % of guest service fees Airbnb takes from guests. If the guest has an inquiry about guest service fees they pay to Airbnb, the guest should take it up with Airbnb directly. Same for the special one-time discount/coupon for 1st time long-term rental (which I've never heard of). If she heard Airbnb is offering, then she should ask Airbnb - because it's clearly not something hosts were made aware of.
My 2 cents - I think it's important to be politely CLEAR about the host's role to guests. If guests have any questions about payment and/or service fees, they need to contact Airbnb directly, not expect hosts to have all the answers.