My wife cannot open links in emails on her iPad. The problem has only recently happened. Any ideas?

You could try a reset, if you haven't done that already. It's my normal solution for everything.
Hold down the Sleep/Wake button and the Home button at the same time for at least ten seconds, until the Apple logo appears. No data will be affected.

After turning the iPad off, waiting for ten minutes, and then turning it back on; it was resolved.