They're going for an unholy mixture of dialect and MSA in this course, and in dialect, sayyidati isn't used and 2ustaadha is. Although it still sounds awkward, because Arabs tend to prefer more specific terms of respect, like 7ajja(-tun) for an old woman, for example, or 2ustaa for a driver of some vehicle of public transit. 2ustaadha would be too distant in many contexts, but it is a valid translation all the same.