بسم الله الرحمن الرحيم
One gets reward of one accepted Hajj if one sees his old parents with love. Allah has given you the chance to serve your old sick mother. Be happy with this and continue the treatment as usual. Read Surah Fatiha (whole surah) 11 times with durood 11-11 times before and after and blow on water and give it to your mother to drink. May she live long! Amen!
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.