Would the questioner be considered sinful if she followed Dr. Nabulsi's fatwa, which some warn against, and would she re-contact you to confirm the answer?

The website is not concerned with evaluating individuals, but it warns against the arrogant tone that casts doubt on those involved in da'wah (inviting to Islam). The questioner can emulate the shaykh whose knowledge and piety she trusts. There is no harm in warning against someone whom others have warned against, for the criterion is the trust of the common person in the scholar. The questioner is permitted to act upon the fatwa of this shaykh, and she is not obliged to seek a fatwa from anyone else as long as she trusts him.