Technically neither cabin crew or ground staff are allowed to lift other people's bags and I think Ken John's response was probably taking that into account. (And yes it is because of back problems).

That said, we'd be really mean not to try and help an elderly person. So I'm sure a passenger will be kind enough to help if the crew are unable to.

But unless she needs her hand luggage then, as the others have said, perhaps best to check it in or put a small bag under the seat in front. Would be far easier for her to access too.