Why on earth is she looking to borrow 6 x salary. That is pretty high and harks back to some of the mad deals around before the crash.
I would be very very surprised if there’s any one out there in the current market prepared to lend on that income multiplier. Sole applicant will generally get 3 x income, joint 3.5 x joint income.
Bear in mind any credit commitments need to come off that £20k also.
Interest rates *are* going to go up at some point in the future and your friend could well find herself stuffed.
Sorry to be harsh but they really need to think very very carefully about this and if it were my friend I would be advising them against this route.