I did this last night.
Last night, I asked my mom if I could teach my sister to masterbate, and she said, yes!
So that night, I asked my sister to come into the bedroom. She said, I'll go to the bathroom to change, but I told her, we're were both girls, so stay here. She was afraid for me to see her naked.
After I saw her naked, she wanted to see me naked. So I took off my clothes. She asked me if she could feel my breasts. My brother came in and we masterbated and it was great!!! So then my sister asked me if she could see my vagina and I said yes. Then I touched her vagina and she has been masterbating ever since.