Depends what you mean by "OK". It is like winstrol. I know a guy who says "Winny is great for women, they use it all the time, it's no problem."
My reply is that you now see lots of figure competitors with virilized faces. Why? Well "women use winny all the time" don't they?
It is known to cause virilizing symptoms among women even at relatively low dosages. Will prostanozol do the same? Probably since it's basically unmethylated winny.
The main question becomes "WHY" would she feel that she needs it? Strength? Hardness? Fatloss? For each of these, I feel there is a better option for a woman. More expensive, probably. Better, definitely. And yet... Women need lower doses of almost everything than men, so price really shouldn't be an issue here.