I think it would be the occasional challenge, but I doubt it would get to the not-fun level.
If the rumors that Mathilde is too blatantly anti-Sigmarite really start swirling, this actually seems like something the Deceiver side of the Coin might be be able to help with. Mathilde could come up with some story about how she actually deeply respects Sigmar but has a hard time expressing it for (bullshit reasons), do a little public penance, and leave everyone convinced, "Ah yes, Mathilde is always acting like she doesn't love Sigmar because she is totally tsundere and embarrassed to admit how she turns to him in her darkest hours. How cute!"
(Mathilde-with-Deciever-Coin)
"I know sometimes I have disagreements with his clergy, but I fucking love Sigmar."
(everyone)
"Well there you have it, she fucking loves Sigmar."
Oh god... now I want this to happen just so we can pull that one off.