Sorry, think I misled you, I accidentally put the arena but it’s actually just the O2 in Kentish Town that she’s going to.
No worries - "The O2 Forum"
I should have picked up on The Kentish Town reference Appologies
Same principle will apply the further away from the centre of London the better,
London parking is a complete nightmare with so many permit parking spaces and and lottery of on street paid parking.
Obviously there are paid car parks, many have height restrictions not suitable for a Cali. - up you'll need to check each car park individually
There are literally no camping places that I know of in central London. - others may know but I suspect you either won't get told or you wouldn't want to attempt it!
It May be better to look at tube to one of the more metropolitan locations outside London. London tube is easy to navigate, there are several apps to assist route planning, you don't need an Oyster card or ticket simply tap in out and out with a bank card at the ticket gate (you'll only get charged upto a maximum amount in one day - can't remember exactly but it about £10)
Parking - Brent Cross has a large shopping centre & open air carpark - open late (bottom of M1) and has a tube station nearby.
Aldenham park has a campsite- easy access from M1 or tube from Stanmore.
Hotel in London?
Heathrow hotel can be cheap & include parking due to competition And is easy to get to London.
Air B&B
The above is probably not ideal but it gives you an idea if you are prepared to get creative
I wish you luck
I hope others will chip in with other ideas