It depends how she was caught.
If it was a camera, then yes, challenge it as it can’t be enforced.
If she was pulled over and spoken to, the NIP can be given verbally so the 14 days wouldn’t apply.
This happened to me, and it was nearly 6 months before I received the fine.
Incidentally, they then proceeded to bill me 3 times for the same offence, so don’t always assume they know what they’re doing.