Sounds like teething poo to me! Also the only time my kids ever got nappy rash was when they were teething as their urine was extra strong and when the ammonia in the urine mixes with the poo it can be quite nasty on their delicate skin. Put a good slathering of bepanthen/amolin/sudocreme on her bottom as a barrier against any urine/poo and make sure you put it on the skin around her vagine too - my girls could get nappy rash almost up to the pubic areas at its worst.