This early love of music has spanned the generations. Cooper's four grandchildren, who were in the audience of the Devilish matinee I saw, are also musical and know her songs well, putting on shows for the family on Friday nights.
Cooper initially qualified as a French and German translator but couldn't shake the need to write music.
"After I had children, I'd be at home with the kids and I'd find I was composing pop songs."
So she made the decision to go back to university as a mature student in 1979, when her two daughters (then aged eight and 10) were still at school, and studied Performing Arts at Middlesex University.
There, she wrote her first musical, which ended up touring through the mid-1990s before landing in the West End.
"One of my tutors saw that I had the ability to compose and we were both mad about the Brontës, especially Charlotte. So I wrote a musical about the Brontës."
It was a later musical, however, that was performed in Prague in 2008, that she describes as the high point of her career. Ghetto 1577, based on the Jewish legend of the Golem (a creature created from the four elements to protect the Jews undergoing persecution in Bohemia in the 16th century) is "very, very special" to Cooper, a member of Marble Arch Synagogue.
"When I was told the story of the Golem by an Israeli friend, I got very excited. At first, I thought I could write an opera, but then I decided I wanted it to have lots of dance in it."
She posted an ad on the website All About Jewish Theatre where she met choreographer Pavel Strouhal. They went on to stage the production in Prague, where the story is set, with Czech actors singing in Hebrew, songs from the Seder such a Ma Nish Tana and Chad Gad Ya.
Cooper says it was "very moving to hear the Czech actors singing in Hebrew" and - perhaps unsurprisingly given the theme - "the music sounded quite Jewish".
This is something she admits she can't really escape from - whether the musical is set in the Jewish Ghetto in Prague, as in Ghetto 1577, or in modern day Clapham in Devilish.
Devilish is the story of an angel who crash lands in Clapham and becomes a reality TV star, battling with the devilish temptations of life on earth before he can learn what it truly means to be human and find love.
When I ask if any of the tunes in Devilish have a Jewish feel she tells me it's not that kind of musical, even though it's about an angel.
Then she breaks away from our conversation to call to her husband Brian in the next room.
"It's so funny, he said 'Yes! Of course! They sound quite Jewish. Something in the Sky for a start, and then a few more.' To me it's just music.
"I tend to write 'Jewish music' if there is such a thing. Everything I write is instinctively Jewish because of my love of Yiddish music."
When Cooper was commissioned to write the music for a stage production of Rudyard Kipling's The Jungle Book in 2013, she wrote what she thought was an Indian-inspired snake dance for the character of Ka, the snake. "But the producer heard it and said that it sounded so Jewish!"
Yiddish music was her first musical inspiration so this stands to reason. "My grandparents used to play Yiddish songs and the melodies inspire the music that I write.
"Then, musical theatre goes back to Yiddish theatre. Lots of Jews were composers of Viennese operetta, where it all started. Jews have always been associated with musicals."
She also loves the Yiddish language. "My maternal grandparents were originally from Poland and my mother spoke Yiddish at home until she went to school.
"My parents spoke Yiddish to each other in front of the kids when they wanted something to be secret.
"But then I started learning German so they had to stop. I can't speak Yiddish but I could understand enough with the German."
So, could she see herself writing a Yiddish musical next?
"I would love to. We don't want the language to die. If someone wants to write the lyrics, I'll write the music!"
So there you go. If you're up for the challenge, so is BB Cooper.
'Devilish' runs until May 29 at the Landor Theatre in Clapham
