A 92-year-old woman, who is cared for by her daughter in Dorset, is being deported to her native South Africa where she says she has no close family.
Myrtle Cothill, who relies on her only child in Poole, has had her application to stay in Britain turned down and has been booked on a flight on Tuesday.
More than 52,000 people have signed an online petition calling for her to be allowed to stay in the UK.
The Home Office said the decision had been upheld by two separate tribunals.
Mrs Cothill - a widow who arrived in the UK on a visitor's visa two years ago - has heart problems, is losing her eyesight and cannot walk unaided.
Her daughter, Mary Wills, and son-in-law David, are unable to move to South Africa because they have no right to live there.
Mrs Wills, 66, says she fears her mother's move back to South Africa could be fatal.
In a statement on the online petition, she wrote: "My mother just cannot live on her own, and emotionally, to her as well as for myself, it would really tear strips out of our heart and probably would kill my mother, and maybe myself as well."
A Home Office spokesman said: "All applications are considered on their individual merits and in line with the immigration rules.
"The decision made on this case has been upheld by two separate, independent tribunals which considered the full range of evidence presented."