Jenny is a 4 year old girl who is seen with her mother as she is worried she may have a vitamin deficiency and is asking about supplements. She has noticed small ulcers in her mouth this morning when Jenny complained her mouth was hurting. Despite this she has maintained her usual oral intake and is otherwise fit and well and has been 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. The is no rash elsewhere but you note a 3mm erythematous macule one her right index finger. Her observations are all normal.
What is her most likely diagnosis?