Berries contain the lowest natural sugar of all fruits but I'm not sure if they suit her. If OK then I recommend a couple of tablespoons of Total 0% yoghurt with a portion of raspberries or strawberries or blueberries or a mixture and a squirt of Sweet Freedom for a tiny bit of sweetness.
They do a chocolate shot too which works well on yoghurt and banana or stirred into some skimmed milk for a comforting drink. All useful for those moments when the sweet tooth demons strike. (I buy it from any of the major supermarkets found either near the honey or the drinking chocolate)
http://www.sweetfreedom.co.uk/index.php/sweet-freedom-original