User blog comment:Derax-Pagani/Chapter 502 Review/@comment-24102956-20160919112456/@comment-193.190.73.129-20160919160355

Can't use her magic against someone stronger is open for denate.

She could affect Natsu, Natsu beat Neinhart, Neinhart resisted her magic. Natsu > Neinhart > Brandi according to this, she shouldn't be able to affect Natsu either.

Maybe Neinhart resisting her magic was due to an enchantment from Eileen. She might've enchanted him to resist Magic.