If you have been feeding your baby with cerelac as her weaning food, there is no reason to believe that the introduction of a new flavour of cerelac will cause any food allergy
Also the amount you mentioned is also very small, ie only one spoon and in general these products are resonably safe.
It is however likely that after applying baby oil, she caught cold
as she was probably left undressed.
Babies are very susceptible to catching cold and hence special attention and care is required to prevent the same.