My daughter purchased (on finance) a fiesta ecoboost 3 weeks ago from Cinch and on Sunday she broke down with an error showing 'oil pressure fault' she pulled over and waited for recovery. They run the diagnostics and told her the wet belt had gone and as the engine was making a noise that it will probably need a new engine!

She contacted Cinch yesterday who said they would arrange for it to be taken to a Ford dealer on Friday. The car is under a 90 day warranty, as she has only had it for 3 weeks would these repairs be covered under the warranty? The breakdown engineer said it definitely should be but I just know they will try and avoid paying for it. 

She had asked to return the car but as it is over the 14 day returns policy I don't think they will let her even though the consumer rights act states it can be returned under 30 days as it is not road worthy. She has asked them to take it back and refund the finance company but they haven't got back to her and it the 30 days will end this weekend.

Can anyone offer any advice?

Yes, get in touch with the finance company and tell them you wish to reject and return the vehicle as it is scrap

You seem pretty familiar with Consumer Rights (which trump Cinch's guarantee) but a handy guide here just in case.

https://www.autotrader.co.uk/content/advice/how-does-the-consumer-rights-act-protect-you-when-you-buy-a-car

It sounds like your daughter did exactly the right thing when the fault occurred. The usual cause of wet belt failure is missed services and/or use of incorrect oil, leading to degradation of the belt. There's no way your daughter could be responsible for that in just 3 weeks.

You shouldn't need to go down this route, but just for information Ford have recently revised their support policy on wetbelt failures - see below.

Hopefully the finance company/Cinch will respond correctly but do let us know how you get on.