I generally agree with Lady Penelope, however in respect of sanding and polishing that is maintenance rather than repair, and it would be reasonable for an owner to do that – the only issue in that regard would be whether the sanding and polishing was done properly, and whether that contributed to any possible damage.
It sounds like the OC has been more than reasonable, it is not clear on what basis the owner is claiming that the whole floor has to be replaced. If it can be repaired, then the OC should proceed on that basis. Owners often don’t understand that if they are claiming something is the OC’s responsibility, then as a general rule the OC decides how to progress it, provided the measures taken are reasonable.
In relation to a cash offer, as Lady Penelope says, do not go down that road. Whatever the OC’s responsibility may be, they should remain in control. For example, what would happen if you paid the owner the cash, and she did not repair the floor, and then sold the apartment?