Responses
Pretty sure she was only 10 in her previous life. It said earlier that she only had until she was 10 years old to live and she didn't recall her past life's memories until she was 10 in this life too so she still has the mental age of 10. They're the same age
Ah yes, I seem to have misread and confused the age at which the game starts for them (15) for the MC's age before she died (10). My bad, and that's good then.
Still, I hope nothing romantic happens till the Prince comes of age, including the MC developing feelings for him only when he's her physical age because otherwise it just seems wrong.