Wife anal.play

My wife has done anal a few times and she always kind of enjoys it but tend to feel dirty afterwards and ashamed that she likes it. I know if she just let go shed probably have anal orgasms and love it. My question, has anyone made their partner cum from fingering her ass? Is there a special technique, can it be done? She seems to like the penetrative part but not like it deep, is that normal? Should I just keep putting the tip in and take it out...maybe she just likes shallow anal? Any advice?
 
Yes I did many years ago.... my wife was having an exceptionally heavy period and although she was really horny did not want to be penetrated....so I started rubbing my hard cock against her butt hole.... as she became more aroused I leaked more precum.... and so she got more aroused to the point where she orgasmed.....afterwards she said she could not believe she could cum like that.
That progressed to anal sex....... where after lots of foreplay and lube I could get into her.....she would cum almost immediately.