Sweetlove, I agree with the comments from tiger31

It's really not as simple as a case of making up a £7 shortfall. It's quite a bit more complicated with benefits.
The carers allowance of £59.75 currently being being received is based on 35 hours per week care so that in itself does not leave much time for employment.

The UKBA ECO will look carefully at any application which is considered marginal/borderline. From the information you've divulged your position is definitely marginal.

As a Fiancee you both should understand that you will not be allowed to work until you have married and been granted Further Leave to Remain.
FLR application will continue to put the finances under scrutiny.

Your Fiance/Sponsor really needs to rethink the overall financial position.
Without that Carers Allowance your Fiance will not be eligible for exemption, which will mean meeting the Income threshold of £18600 per year.

Sorry it's not really what you'd hoped for. You and your Fiance need to discuss together.