Well, IMO $200 is a huge favor to you. How long will she have to spend on the cake? I would ask her what she wants $ wise and go from there. I would offer her free advertising at the event (if that is what she wants) as a bonus on top of the cost plus offer to pay for any supplies she needs.
Katie, mama to a pair of boys one little and one not so little.
"No American president has ever supported a major expansion of civil rights that has not ultimately been adopted by the American people - and I have no doubt that this will be no exception. The march of freedom that has sustained our country since the Revolution of 1776 continues, and no matter what setbacks may occur in a given state, freedom will triumph over fear and equality will prevail over exclusion." -Michael Bloomberg