"Her mother" is the subject. We use inversion with "as" in this sense, or we could say (with the same meaning), "She is tall, and her mother is too." This is absolutely *not* the same meaning as "she is as tall as her mother (is)."

The subject of “is” is “her mother.” A better expansion of the sentence will help you see why: “She’s very tall, just like her mother is very tall.” Here, “As” = “just like”. Your sentences about the figure use “as” in a different way. Here, “they saw as” = “they believed to be”.

Hello! The first sentence is correct: "She's very tall, as is her mother". "as is" means "just like". So the sentence could be written like this: "She is tall, just like her mother". The sentence "a figure they saw as having been close to the government" expanded would be written like this: "a figure that they thought was close to the government before". The two sentences don't have the same structure - in the first sentence "as is" is in the present tense and in the second sentence "having been" is the past participle form of "have been". I hope that helps!

Well, I should say even the first sentence doesn’t make sense to me! It should be “she takes after her mother”