Before I address this question, I want to point out that this is a poorly written passage. It is riddled with grammatical and factual errors:
- the Seneca Falls Convention happened in 1848, not 1948
- "considered to be" is not idiomatically correct
- "100 of the approximate men and women" makes no grammatical or logical sense
- "Alice Paul was forced to resign... and started her own..." needs a comma before "and," because these are separate independent clauses

It is a bad idea to study from any source that takes so little care in writing its passages. You should only study from reputable sources that are very like the GMAT.

All we're told about Alice Paul is that she was forced to resign from NAWSA in 1915, and she started her own organization, which used mass marches and hunger strikes. As always with RC, don't look for the right answer; look for 4 wrong answers instead.

A. We don't know her views on NAWSA, we just know that they kicked her out.
B. The 15th Amendment passed in 1869; her organization was founded in 1915. Impossible.
C. If she used public protests (mass marches and hunger strikes), it's safe to infer that she thought they were effective. CORRECT
D. A "would not have been possible" statement is hard to prove. Even if she was a key player, it's possible that it could have happened without her under different circumstances. Unless the passage had said something like "she's the only one who could have done it," this kind of statement will be a wrong answer.
E. The NWSA and AWSA united as NAWSA in 1890. Alice Paul left NAWSA in 1915. It's possible that she was a member of NWSA before 1890, but we don't know that for sure.