senior judge denzil lush said elder sister could be jailed for attempting to alter a legal document , so she could gain greater control over her mother 's money .
the mother , who has dementia , lives in a care home in stoke mandeville , buckinghamshire .
she owns a £ 600,000 house , has savings and shares worth £ 100,000 , and has an income of £ 1,200 a month .
the ruling was made in the secretive court of protection in which hearings are routinely closed to the public .