Well, I like challenging games, so here's my gripe:
The trouble withe the "defend the capital" rule is that the AI seems to have no clue. The last couple of games when an AI has launched a ship, I've taken his capital with ease despite him having many units empire-wide.
In my last game Churchill launched, and I was closing in my armies from 2 directions. I took London, which had just 4 units defending it. His 3 closest cities OTOH, all had at least a dozen, with York for some reason having about 20 ( I guess he thought I was going for that.)
Seriously, the AI needs a "defend the capital at all costs" mode after launching an SS. It doesn't seem to even know about the rule now.
edit: to OP: Boudica doesn't declare at pleased, IIRC which is only +3 under normal circumstances. You clearly weren't doing that much to keep her happy .. or you were doing lots of bad things to offset the nice things. Of course if you had vassals she didn't like, then thats a different story.