If she has worked in the UK, request form E301 from HM Revenue and Customs. She will need to take this, along with any and all documentation relating to her working history and illness, to her local INEM (the Employment people) who will probably direct her to her Social Security office. In the interim they may be able to arrange a minimum payment, as she is over 52 and has no income. Form E301 will help in claiming sickness benefit, as it tells them her UK work history.
Her sickness benefit should not have been stopped if she is signed off by a doctor as being unable to work.
Where does she live? I would suggest she went to her local workers Union (UGT or CCOO) for further help and advice.