iv just bought a female bearie as a birthday prezzie for my male (i wanted him to have some company) they seem to be getting on but she keeps trying to eat her rock. iv never seem any lizard do this before. has anyone else witnessed the weirdness??

Sounds like she's trying to increase her calcium levels, some lizards intentionally eat their substrate, or in your case rock, to extract the calcium from it and increase their body calcium levels. I could be wrong but try increasing her calcium/phosphorus intake a little and see how she does.
Are you supplimenting her with calcium/phosphorus, and providing her with uvb lighting? If so i don't know what else to suggest.

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It's not really a good idea to keep a male and female together permanently. The poor old female will be constantly harassed by the male and become totally stressed.

Well she has the correct uv bulb and we do dust the worms and feed the crickets etc on calcium suplements as this was my first thought. I did have to remove the plastic plants too as she seemed to prefer these to the normal plants.

As for mixing them together the viv is large with plenty of hiding places etc if necessary, we were going to get the male neutered too if necessary. Although Iv never had trouble with them living in pairs before.