She has been sick for three years and did not fast

Allah has forgiven the sick person for delaying the fast,
because Allah, may He be glorified and exalted, says (interpretation of
the meaning): “and whoever is ill or on a journey, the same number [of
days which one did not observe Sawm (fasts) must be made up] from other
days” [al-Baqarah 2:185]. This is a favour from Allah, may He be
glorified and exalted; He has allowed the sick person not to fast and to
delay making up the fast until he has recovered. Hence He says
(interpretation of the meaning): “Allah intends for you ease, and He
does not want to make things difficult for you” [al-Baqarah 2:185]. If
Allah heals you, you can make up the fasts that you missed. Praise be to
Allah. 

But if the doctors have determined that there is no hope of
recovery from this sickness and that it is ongoing, then you have to feed
one poor person for every day (that you do not fast). 

Old men and women who are not able to fast must feed one poor
person for each day, giving half a saa‘ of dates, rice or other local staple
food. This is equivalent to approximately one and a half kilograms, which
should be given to some poor people. 

But if a person is waiting to recover and has the hope of
recovery, he does not have to feed the poor; rather he should wait until
Allah heals him. When Allah heals him, he should make up what he has missed
of fasts, even if it is several years, because he had a legitimate shar‘i
excuse. No expiation is required in this case. End quote.