My mum suffered from multiple sclerosis and was wheelchair bound by the time I was 11 and more or less housebound by the time I left school. When I moved into my own flat at 21, my parents lived between my flat and my work so, I would pop in about three nights a week and would call every day.
Once I got married and had DD1, I would visit my parents several days a week and continued to call daily - my mum was unable to do much but she loved me and my DD and enjoyed watching her grow and begin to interact.
Soon after I had DS, my parents moved to the next village to ours; unfortunately my mum died six months later and never got to meet DD2 and DD3.
Our relationship wasn't a carer/patient one, simply a mother/daughter relationship. My DM was never able to physically help me with my DC but provided me with confidence that I was doing the right thing. I would have loved the opportunity to go places with my mum, but more than anything, I loved our chats, sometimes serious, sometimes comical.
For those who do have a close relationship with DM or DD, providing it is not to the exclusion of other relationships, I would say enjoy every minute - you never know when it may be snatched away.