On the radio the other day I heard a song by the Viennese songwriter Hugo Wiener, sung by chanteuse Cissy Kraner: Eine verzwickte Verwandtschaft (Tricky relatives). Could it be ...? Yes it was. The last line was "I'm my own grandma".
Wiener died in 1993, and this song seems to be from the Seventies. I suspect it is an adaptation of our song above, though so far I haven't found proof one way or the other.