If you become incapable of managing your own affairsThis has to be a classic example of Joseph Heller's Catch-22*. For if one is not capable of managing one's affairs then one is hardly likely to be able to digest a long Government letter let alone send a reply. And if one does make a reply to say that one is not capable, this surely would be deemed proof of capability.
We aim to sidestep this conundrum by explaining that she is not capable of managing her affairs, but that we are.
* For those unfamiliar with the origin of this now well-known phrase, it was the trap that ensnared Heller's protagonist - an air force pilot in the second world war desperate to avoid going on another, extremely dangerous, mission. The only outlet was to plead insanity but since only a sane man would make such a plea, it was automatically rejected.