Your wife needs to find out who her plan administrator is. Small districts often self manage, but the larger districts hire an administrator since paperwork requirements can be huge. If the district is managing her 457/403 plans, she should speak directly with that person--more than likely someone in HR or the business office. I'd ask them why they have the requirement, and I would ask where in the districts plan documentation it specifies that. I would want to see the actual document. If they can't point to the document and show where it is required, then they can't require it.
If her district uses a third party administrator, you have to get in touch with them directly and pester them.
In the long run, it may be of no avail--you may just have to pay someone to certify your doc. But once you have the account set up contribution changes should not require additional signatures.
I'm a teacher, and have both a 403(b) and a 457(b) with my district, and go through a third party administrator.