Charlotte Caldwell attempted to bring in medicinal cannabis oil to the UK for her 12-year-old son Billy but it was confiscated at Heathrow airport on Monday after a flight from Canada.
He was taken to Chelsea and Westminster Hospital on Friday after the frequency of his seizures increased.
Ms Caldwell said on Saturday that Billy had two seizures overnight but he was now stable and asleep.
"Billy had two more seizures overnight which is putting him further into a crisis situation."
The Home Office said it is in contact with doctors treating Billy and is carefully considering treatment options.
"This medicine was anti-epilepsy medicine. He has to have it every day. He needs it as soon as possible. We are hoping for a resolution today,"
Ms Caldwell said, speaking outside the hospital.
"I am confident we are going to get this done. The medical teams are working closely with the Home Office. We are praying for a miracle."
Sinn Féin MP Órfhlaith Begley welcomed confirmation that Billy would now get his treatment.
"Billy should never have been put in that position. The treatment was clearly working for him and he deteriorated badly once it ended, yet it still took intense lobbying to get the Home Office to reverse this cruel decision."
Ms Caldwell praised medical teams at the Chelsea and Westminster Hospital. She said: "The staff here have been amazing. He is getting the best medical care in the world. I cannot thank the staff at the hospital enough."
Billy, who is also autistic, with pronounced communication difficulties, suffered back-to-back seizures on Friday after being seizure-free for more than 300 days when he was previously given the cannabis oil, according to his family.
Billy, from County Tyrone in Northern Ireland, was given a prescription for medicinal cannabis oil last year to help treat his epilepsy - the first time the drug had been prescribed by the NHS.
But the boy's doctor was told by Home Office drug enforcement teams to stop prescribing the medication, which Ms Caldwell credits with keeping her son's seizures at bay.
The family had planned to return to Canada if they could not get the medicine in the UK but say Billy is now too ill to travel.
A Home Office spokesperson said: "We are deeply sympathetic to the extremely difficult situation that Billy and his family are in.
"Billy is in the care of medical professionals who are best placed to assess the care and treatment that he requires."
"The Home Office is contacting Billy's medical team.