A few generations ago, brushing hair was a crucial, and pleasurable, every day routine for many women. These days, few people have time for lengthy sessions in front of the dressing table, but even modern hair needs a good brushing and some attention now and then. Easy enough, unless you have a shoulder injury or arms that don’t like being raised above shoulder height, in which case there’s nothing easy about it; getting to the top of your head to shampoo, to brush, or to comb can seem like climbing Mount Everest (but with bad hair!).
Here is a set of tools that might solve the problem. This nubby hair washer is long-handled, and has just 
the right surface for a gentle scalp massage while you shampoo. It’s long enough (14 and one half inches) to extend your reach significantly, and the handle looks nicely ergonomic and easy-to-hold. I’ve seen back scrubbers that looked similar (love those nubs!), but this wand has a bend to make getting to your scalp (and following the curves of your head) much more feasible.
The website that offers this “Long Reach Hair Washer” also sells a long-handled comb and brush, each with a 14 inch handle. Search on ‘comb’ or ‘brush’; you won’t find the items by searching under ‘hair.’
These tools aren’t cheap — 23 to 25 USD apiece, but when an 89 cent comb just won’t work, they could make all the difference.
(Special thanks to Jan, who tipped me off to the website!)