How much to "tip" wedding photographer/friend?

Kelsey

I say tip in quotations because she has said the only pay she wants is to buy the memory card. We're both low income, and she's buying a new camera so that she can do my pictures (she has one but can't figure it out). She's the only friend i have that has taken a professional photography course, and i asked her because i can't afford an actual photographer. But i don't feel right just giving her nothing for it. HELP!