Figen Murray has campaigned for higher security at public premises.
Her son Martyn Hett, 29, was one of 22 people killed by a suicide bomber at an Ariana Grande concert in 2017.
She has campaigned for the introduction of Martyn’s Law, which would require venues to take enhanced steps to keep the public safe from attacks.
But she fears time could run out for MPs to approve the Bill before Brits go to the polls.
In a letter to the PM, Figen, from Manchester, wrote: “Nearly a year and a half after we spoke, and seven years since my son was murdered, we still await the introduction of this law.
“The slow pace of progress risks the Bill failing to get through this parliament and I urge you to please commit to introducing the draft Bill in time for the next anniversary of Martyn’s murder in two months’ time.
“These anniversaries are not just dates. They are a point in time that will forever haunt those families that have been hurt by terrorism.”
Last month the Home Office launched a consultation into the proposed law.
Last night a spokesman said: “We are reviewing its findings to ensure all feedback is fully considered, with a view to introducing the bill as soon as possible.”