No No No No!!!!

The oxygen levels in aeroplanes are reduced during flights to save fuel, so no wonder vunerable people may be affected.
It would feel like fainting.
It is probably no more than that..
Amazingly even BA do it to save fuel so I expect Easyjet are into any tricks to reduce costs.

I think you're mad to contemplate a long long drive which would be more stressful with frequent loo stops and related anxiety.

I wouldn't fancy it in the back of a car knowing I'd put everyone out!

Perhaps I could arrange to have someone meet Mum and Dad or one of us could at Gatwick if that would help.
A taxi is booked isn't it and they've still got to go home haven't they to get the car otherwise they're stuck in Wheatley without being able to please themselves.

It would be better for Mother to come home a few days earlier allowing time to recover from the journey.
She wants to be feeling all right for the party doesn't she?

If it was me, I'd come home a few days early on the Eurostar/TGV Avignon to London.
I'm sure she'd be fine on a train.
They do do offers and deals and I've heard on radio4 it's cheaper from France.

love Steve