My 语感 is telling me the part in bold is not correct. Let's simplify the people, as it doesn't affect the grammar:
It like it's trying to force "他受奶奶的影响" to be the subject of the sentence. I would instead expect something like:
Question: Is 孝文帝受她的影响很大 grammatical, and if so, what is the underlying grammar structure?
Edit: Thinking about this a big more, it appears to be a 杂糅 grammar issue. Overlapping 他受奶奶的影响 with 奶奶的影响很大.