A hall rail is a continuous rail mounted to the wall along the route, so she has something to hold from the bedroom door to the bathroom. It does its job only if the screws hold under her weight when she pulls. Everything else about the decision follows from that.
Local option: New Plan Care gives families in the St. Louis area in-home help so a parent can stay home: companionship, help with bathing and dressing, meals, and overnight care. Call (314) 405-0887.
Find out what the wall is made of
Knock on the wall and listen. Hollow sound usually means drywall over framing. A solid, dense sound can mean plaster over lath, or masonry. Plaster and lath can crumble around screws, and masonry needs different anchors. Note the wall type at each spot where the rail will go.
Check the studs and the fasteners
Use a stud finder and mark the center of each stud with pencil where you can see it. Then confirm the position with a small test hole or a second check, because a stud finder can misread. Compare the fastener length and type against the instructions that came with the rail. If the instructions list a fastener, use that one.
Decide who mounts it
Do it yourself if the rail can go into studs, you have the tools already, the hardware is the kind the instructions list, and you can work in daylight with a second person to hold the rail level.
Hire it out if the wall is plaster or masonry, if the rail must anchor into something other than studs, if you suspect wiring or pipes behind the planned spots, or if the run is long enough that keeping it level becomes a two-person job with a ladder.
Questions to ask a hired installer
Ask what wall type they expect to find and what they will do if they find plaster. Ask who patches and paints the holes, and whether the patch is part of the price. Ask what happens if the marked spot has no stud. Ask whether they will test the rail with a load and show you the test. Get the answers on the quote.
Test it the right way
After any mounting, have a second person pull on the rail at several points, slowly, to check for movement. Never test by putting her weight on it for the first time. Check the rail again after a few weeks of use.
What to write down
Write the wall type, stud positions, fastener type and size, and who did the mounting. Note the spots you tested and what you found. Keep this note with the instructions. Local options for help after a fall are listed on the local help page if you need someone to come out.