The 15-year-old, who can't be named, was found guilty of murdering Elizabeth Edwards, 49, and Katie Edwards, 13, at their home (below) in April this year.
Elizabeth regularly attended St Paul's Church in Spalding, singing in the choir and helping with youth work.
The pair were stabbed to death by the girl and her 15-year-old boyfriend, who admitted murder at Nottingham Crown Court.
They're believed to be the UK's youngest ever couple facing jail for murder.
Rev Mike Chester, vicar of St Paul's, said: "The horror of it, the loss of it, is going to stay with this congregation for a long long time.
"They were part of us and loved very much.
"We've put a small plaque up, not that we need that, and we have their photographs on the side altar and we light candles on Sunday morning as a sign of their presence with us."
