I would suggest have her return it to you and then refund it. I can appreciate the no return policy on custom goods, I have the same, but in cases like these, when something is apparently wrong even after you checked it so meticulously, I would want it back to see for myself. Unfortunately there are people out there who will lie to try to get a refund and keep the item for free, so I'm quite firm about things like that. If there are problems I would rather replace the item and have the original returned.
There is a good chance, IF she is one of these people, that she won't want to return the item in order to get her refund, and in a case like this with an item with such a specific purpose, you have to wonder why she would want to keep a piece that was apparently faulty.
So, personally, I would say ask her to return it and either offer a refund or offer a replacement, and then when you receive it you can see for yourself if there was anything truly wrong. If she's just trying to get it for free she probably won't want to return it before she gets her refund.
It's also possible however that she's just being an overly picky bride - many (not all, but a lot) brides strive for perfection for their wedding, even on items that no one else would know was 'imperfect', and sometimes they can be a little irrational and unreasonable. I can of course understand that, but at the end of the day that's what causes a lot of bridal stress, and stress for sellers like you as well.
