Changes that alter the appearance or surface of the common property (in this case the wall opposite the lift) require approval by special resolution at a general meeting.
Ideally, she should get a couple of quotes (the Committee may prefer to get it’s own quotes, but as a Committee member, I find it helpful if an owner who wants something done contributes to the work), and she would make a request in writing to have the rail installed. She might consider putting forward several options with prices: a standard “disability” type of rail or something stylish and in keeping with the general decor that would still meet her needs.
I’m not sure what she should do if the Committee ignores her request (it’s important that the request is in writing, and dated). If there is a strata manager, she can get advice from that person on next steps if she doesn’t hear from the Committee. If all goes well, a general meeting will be called and a motion put forward to install the rail.
If the Committee is being difficult, an offer to pay for the rail and installation might help.