When cats "go" outside their boxes, especially ones that have always previously used them, it could be signalling a serious health concern. They will do this as a sign to their humans or possibly because they can't control it.

Possible problems associated with this are

Blocked Urinary tract,
Bladder or kidney infection
kidney stones
crystals

This could be caused by food that is too high in certain mineral contents, high Ph level or acidity of urine, or water too high in certain mineral or "Ick" content.

Tell her to please not assume this is a behavioral thing. Her cat could be trying to signal a serious problem.

I might add that some of those problems, if not treated immediately can become deadly. Especially the blocked urinary tract. (their bladder could litterally "explode")

If it is a bahvioral problem, consider this...
Is the litter box in a conspicuous place? a high traffic area? Has it been moved repeatedly or set too close to food and water bowls?
All these things too will make a cat try to use something other than his box.

The perfect location would be in a quiet, kind of hidden corner nowhere near food or water dishes. She may try the ones with the hoods too. Cats like those.

Wish her luck for me and please keep us posted!