Yvonne's stories are quite unusual. By her own admission they are pure stroke stories for people with a sadomasochistic streak. At this they are superb. A good solid 9 on the stroke scale.
They have a number of spelling and grammatical errors, but these are trifling and expected in a stroke story. So technically they are well within what could be expected.
And yet they are truly well built stories with a plot and most interestingly good character development. Personally I do not normally enjoy first-person narratives, but Yvonne gives her heroine a true personality. We get to understand not only what she is doing, but why. While we may be horrified by the actions themselves, if there is any voyeur in the reader (and I for one think there always is), s/he cannot help but be excited by the heroine's response.
Likewise the husband ("Rob"): his is a bit part, but is critical. The heroine carries out her role not only because she craves the intensity, but because it pleases her husband to be able to watch. This is complex interplay which Yvonne handles very well in a what is really a quite short story. So for plot an 8 - it would be higher if this was a longer story.
Appeal to the reviewer is obvious. A story I will read again and again deserves a 10. This is an author that should publish more.