ETA, to be fair, she did give you 3 months notice and you have known for 12 months that the rego would be due, so I dont think that you can really play that card
We usually pay 6mthly on our Rego LTD. When we got our rego bill we discovered that 6mth payment was no longer an option. I have a punching bag post about it. We also have not had 3mths notice about the cost of going. I thought it was just the standard night tour, not through an actual tour group. We only found that out 2 weeks ago.