Depends on which conspiracy theory you believe.
Why do you need to believe in any? All she had to do is put her seat-belt on!
The car crashes, Dodi and the driver dies, Princess Diana survives, after recovering from the shock and berating the photographers for just taking pictures; she recounts how the driver was driving like a man possessed since leaving the hotel.
She returns, to the UK shaken - but after awhile stablised by the company of her sons, she re-enters public life and continues with her charity work
Meanwhile, Dodi's Father (as per OTL) wages a campaign against the assination of his son to prevent a marriage between him and the 'Princess', her responses were he said from someone who had been 'got it' - after all 'why was it' he said 'she put her seat-belt on?'.