ANSWER:

She has to be in the state of wudu to pray. If she’s unable to get up and pray then she can definitely pray while lying down in bed, due to old age. 

Somebody should help her do wudu by bringing water to her or assisting her to the washroom as they would when she has to answer the call of nature.
If she’s counted as insane, who cannot recognize day from night then praying is not fard on her until she becomes sane. 

My granma is 80+ or close to 90. for last couple of week she is sick missed prayer. she is on bed can’t move. her behaviour became a bit abnormal. she normally used to pray 5 times a day. my uncle said to her u dnt hv 2 do d wudu or sit to pray(as u r unable)& u r like a baby. is it correct that whn people reach really old age they r being treated lyk baby?