Oh she's lot older than 5-6 weeks. no need for kitten formula at all. Kitten food is what she needs. looks happy and content. She's very cute!! She does not look feral at all. She was someone's kitten who either got lost or whom the owners decided they didn't want her any more. She looks healthy from the photo.
She might be 2-1/2 to 3-1/2 month old.