latest versions of FF don't display things properly
They do if it's correctly coded... problem is, some people can't be bothered to do that.
She might well find that the bank website or cable company website is set up to work properly only in IE and she might have to try IE just for that 1 site
A new pair of hands might come in useful to make that possible - IE is the least disability-friendly browser of all because it doesn't support stickykeys etc even when that's enabled for the rest of Windows.
No, I don't know why either.