Can a five year old girl get vaginal thrush?

Yes. There are many things that can contribute to developing thrush that is independent of your age. For example: wearing tight clothing that prevents natural ventilation taking antibiotics using certain products like bubble bath.
YES. Monilia infection just like any fungus likes dark and wet locations. Your child can get the infection if genitals are not cleaned thoroughly with soap and water.

Related Questions

Can it be that a five year old girl have vaginal thrush?

Possibly. It is possible, given her age, if you are concerned i would immediately have her evaluated by her pediatrician. Read more...