If your mum gets really interested in cycling, depending on what her health problems are, there are adapted bikes she might be able to use. Also there are schemes about I think where able bodied people and people with difficulties share a bike. I don’t know the names of the charities or company’s that do these, but I expect an internet search or asking a charity would get you some info.
This guys done a couple of nice modern cycling books
http://www.alastairhumphreys.com/
If she likes computing she can download Thomas Stevens “Around the world on a bicycle” for free at
http://www.archive.org/details/aroundworldonbic01steviala
http://www.archive.org/details/aroundworldonbic02stevrich
He cycles around the world on a penny farthing in 1870 or so. You might need to be a keen sort of reader to get through it, but I found it very interesting – lots of stuff on how local people lived at the time. You can also get it as a paperback from Amazon.
http://www.archive.org do quite a lot of interesting downloads related to cycles, so worth searching on there. Also for other topics you mum may be interested in, esp if she likes the past/history/how people used to live.