You can certainly direct-message the author on her home page (http://food52.com/users/5488-pati-jinich) and ask her about the omission. She can edit the recipe and correct it.
I'm not the author of recipe but from the photo of the stunt tostada I would suggest either queso fresco or cotija (which is a little firmer). Cacique is a good brand for either.
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In addition to queso fresco & cotija - farmers cheese is an option.