Here is a young mother who reveals her motherhood status to me. It was very exciting to see her! She’s two years old and she has just had her first litter.
In very young mothers, however, unless they show you their bellies, it is almost impossible to tell that they are lactating: the mammary glands are compact and don’t “show”.
On the other hand, older mothers very often do reveal their status as mothers. By the time a coyote has aged and has had several litters, the mammary glands sag more, and if you are looking for it, you can see what is going on.
More on lactating mothers: https://coyoteyipps.com/2010/05/26/lactating-mothers/