Ok I have repotted her this evening, bigger pot, fresh soil and lots of perlite for airing.
The roots were very wet in the old pot, and there was LOADS on the bottom of the pot. I gently knocked all the soil off the roots and what appeared to be crap roots that may have had rot just fell off - not many came off but the whole pot was gholding SOOO much water, it was sodden - perhaps bad drainage caused it, maybe the roots were suffocating?