OK, that's what I was afraid of for you. On her 16 hour layover, think of checking main baggage through in MAN and just going into town and looking around if its daytime - underground to civilisation is 1.40 S$ each way and takes about 30-40 mins worst case - its brand new and only opened a few weeks ago. She should make sure she has her boarding card (probably issued in Manchester if not at the transit desk in Singapore).
Remember NO chewing-gum allowed in Singapore, high fines; and death penalty for drugs of any kind.
