Can an 11 year old girl start a pet sitting service and if so how can she do advrtisement signs ect and how much should she charge?

I know a girl named daphne Scott and she started minding dogs for her friends at a young age and then she started minding everybodys pets and charged them for about around 10 euro a week. I'am not pretty sure but she is now a teenager and has lots of advertisements around her home and she named it Precious Pets. She also has a shop at her home and sells items there and she sells puppies.