Sentence Correction

Hi,

Although the question is discussed in many threads earlier, I am opening a new thread because all threads, I found, are very old to discuss here and may not interest readers to take up discussion.

Here we go with the question:

123. She was less successful after she had emigrated to
New York compared to her native Germany,
photographer Lotte Jacobi nevertheless earned a
small group of discerning admirers, and her
photographs were eventually exhibited in prestigious
galleries across the United States.
(A) She was less successful after she had
emigrated to New York compared to
(B) Being less successful after she had emigrated
to New York as compared to
(C) Less successful after she emigrated to New
York than she had been in
(D) Although she was less successful after
emigrating to New York when compared to
(E) She had been less successful after emigrating
to New York than in

OA C

Question: I want to understand how the modifier in C (Less successful .. she had been in) is not a clause when it contains a subject (she) and a past participle verb (had)? I initially marked C as wrong because I understood the modifier to be a clause. This gave me an impression that C creates a run-on sentence (two clauses joined together with a comma).

Could any expert please help me understand what I am missing here?