She looks like a very pretty Easter Egger! Except for her bright yellow legs...?
I don't know what it is about certain "breeders" selling their mystery birds and cockerels as purebred pullets. I have heard this exact situation happening countless times. A true breeder will know exactly what they have, and be able to cull their unwanted cockerels themselves instead of pawning them off on others, or at least be honest and sell them as straight run. I personally would never trust a backyard breeder or their biosecurity either.
You might be better off keeping just one cockerel and getting more pullets. Here's a good article to help you decide:
https://www.backyardchickens.com/articles/selecting-good-flock-roosters.74719/