its a bit difficult to mange, but gets her off each and every time. With her in "doggy" instead of being directly behind her on my knees I'll have one knee planted between her legs and my other leg is thrown over her and my foot planted for support more or less beside her. You are still entering from behind, but almost in a sideways fashion. I've found this also gives deeper penetration. Now here's why this works so well. It frees up your hands as you've got solid support. Now with one hand reach around and cup her pelvis so that your fingers are covering her clit. With this you can apply pressure and motion giving direct clitorial stimulation while still penetrating at a decent rate. With the other hand it's quite easy to slide a lubed finger or two or however many she likes into her backdoor. Typically once I enter her ass with a finger or two while fucking & stimulating her clit it's only a matter of seconds before she crashes into orgasm. From there I end the the anal stim, but continue with clitorial stim with more of a just pressure rather than movement. Your strokes into her should provide movement enough for continued stim on an already sensitive clit. It varies im sure, but my wife has learned to take the continuous stimulation and just ride waves of orgasm after her first big one. Works for us, maybe for you too.