Jenny is a 4 year old girl who is seen with her mother who has noticed small ulcers in her mouth this morning. Jenny has complained her mouth was hurting, but despite this she has maintained her usual oral intake and is otherwise well and is attending pre-school as normal. She has no other medical history and is up to date with immunisations. She complained of a sore throat a few days ago but this has since settled.
On examination there are small yellow-grey ulcers in her mouth with an erythematous halo, and her tonsils look normal. There is no rash elsewhere but you note a 3mm erythematous macule on her right index finger. Her observations are all normal.
What is her most likely diagnosis?