Then, there is only one thing you can do here.Irisviel already having a husbando doesn't discredit her for being voted for as a great Waifu though, it might actuall be a positive point for her. We could say that Jeanne doesn't have any experience in couple matters and this would be an argument for voting Irisviel who isn"t as inexperienced.
I mean i see what you mean, but Jeanne being available seems irrelevant to me.
By the way, "discredit" sounds way too harsh. I didn't discredit Iri in any way with my post, just provided some points why Jeanne might appeal to you (or others) more. In your case, they didn't matter. It's no biggie, that's the beautiful world of different tastes and preferences.
Introducing an inexperienced person - who has beautiful character traits and huge waifu potential - into the world of romance, love, passion and devotion can be interesting too.
P.S.: I didn't vote yet, lol.