Janet Ajao said she was "deeply shocked, saddened and numbed" by what her terrorist son did during his rampage in Westminster.
The crater could hold more than 6,000 bodies, but landmines scattered around it hamper efforts to recover the remains.
Returning extremists could be back in the UK awaiting instructions on when to attack, a security expert tells Sky News.
Sky News correspondents report as the Iraqi army closes in on the final Islamic State urban stronghold in Iraq.