Dippy .. fight them all the way .. I have just had a minor claim settled .. its been running since DECEMBER !!!
They offered 50/50 "as there are no third party witnesses" .. I have been strongly pointing out the photographic evidence of the damage, and asking the same question a zillion times "how can I drive into someone when the damage is to the side of my vehicle .. my vehicle does not drive sideways".
On the last occasion I INSTRUCTED ( and I mean that word) my insurers to instigate Court proceedings .. or I would as the Burden of Proof is "The Balance of Probabilities" and given the photo's of the damage .. the probability is the guy hit me. I gave them permission to quote me to his insurers.
The claim was settled within 2 weeks in my favour, I recieved a cheque for my exces and a letter confirming the reinstatement of my No Claims bonus within a wek of the settlement.
It takes a while.. but stick to your guns .. you have the rules from the Highway Code .. she was in the wrong.
my basis for this is one line of your description...
I indicated left to come off the roundabout and went across the outside/left lane of the roundabout headed for the right of the two exit lanes.
IMHO you did not change lanes as you headed for the RIGHT lane of the two exit lanes .. and crossed the left lane of the roundabout as you had to...if you had gone for the left lane it would be your fault for changing lanes.
I apologise if I have misread your description