My wife was recently given a technicium cardiac stress test and when we had a couple of friends around for dinner one of them (a geologist) bought out a Geiger counter and managed to get counts 4 metres away from her. Two centimetres from her body the counter registered almost 10 microSv per hour, which was higher than my friend had ever seen before!

Should I be worrying about this, as I guess it stays in her body for a while. I guess that she’s now been exposed to the radiation, but should I stay in a different bed room for a while, as my friend says that the counter will go down in a few days ?

No you should NOT be worried by these results, especially as she has recently had a nuclear treatment, it's to be expected and well within safe limits.