It can't recur Ruthie because having had it provides life-long immunity, but sufferers can still experience similar symptoms which should clear up in a few weeks.
Glandular fever can recur/relapse. The virus basically stays in your system if you don't fully fight it off after the initial infection. Most people recover fully, but in some cases it is severe and some people either find they suffer with fatigue and other symptoms permanently - I think this is what Robin Soderling's experience has been - while others can suffer relapses, which is what my own experience has been.
The relapses are often worse - my first relapse was worse than the initial infection. The second relapse about eight years later was very sudden and instantly debilitating but lasted for a shorter period of time. Relapses as you get older can be very aggressive.
I hope Heather is ok and that her symptoms aren't connected to any relapses, but a real shame for her to be ill/injured again.