Lucy Cope's son Damian, 22, died after being attacked outside Brown's nightclub in Covent Garden, in July.
His killers have never been found and she is now calling for guns to be taken off the streets, tougher sentencing and a ban on the sale of imitation guns.
She had threatened to stage a two-week vigil outside Downing Street but Home Office minister Bob Ainsworth persuaded her to postpone her protest.
To promote her message Miss Cope founded the Mothers Against Guns group which marched in south London earlier this month.
Speaking to BBC London she said: "What I have tried to do is to bring public awareness to the gun culture we now have in this country, in London especially.
"It has been heartbreaking, but these mothers have been united... saying 'enough is enough', and we don't want anymore killings on our streets.
"And to the people selling these imitation firearms I say, 'take them off your shelves.
"They are converted to become lethal weapons and people are losing their lives."
Damian Cope, from Southwark, south London, left the trendy nightclub on 29 July after receiving a call on his mobile.
He went outside and was shot once in the stomach with a small calibre handgun. He died in hospital.
Miss Cope said her meeting with Mr Ainsworth had been positive and he was listening to what the community wanted.