I have introduced two female friends to enemas. I have found that most women are okay with it if the first time it is a surprise, like you stated.
I tied her up to the bed with her arms above her head and her legs tied tight to her chest. I blindfolded her, of course, and began to tease her by using a feather over her entire body. I eventually went to a Wartenburg wheel, which really blew her mind.
After playing with her clit and bringing her to the edge, I gently started playing with her rosebud and slowly entered her backside with my finger first, testing her reaction. She was dripping wet (figuratively, that is). When I finally inserted the nozzle, I screwed her with it at first, then let the warm water flow. All I can say is WOW. When she finally came, she exploded.