Sabrina Moss was shot on Saturday evening on Kilburn High Road as she celebrated her birthday and later died in hospital of her injuries.
A man was arrested at St Pancras station on Tuesday evening on suspicion of murdering Ms Moss and of the attempted murder of another woman who was injured in the shooting and is still in hospital.
“Our family has been devastated by this horrific incident that has changed our lives forever,” said Ms Moss’s parents Andrea and John in a statement released by the police.
“Sabrina was a fun loving girl who made friends wherever she went. She was a lovely daughter and a perfect mother to her young son, whom she adored.
“She cherished working as a nursery teacher and treasured working with the children, who undoubtedly will miss her dearly.