Assuming you are selling as a non-resident (which your posts would suggest) then you will have the 3% retention held back against CGT liabilities. In practice, this can be used to pay off (or withheld until you've paid) all your back taxes...so...whether you actually WANT to get away with it probably depends on the figures involved

The Notary is required to satisfy himself and the purchser that all property related taxes have been paid and if they have not then this will be taken from the retention. This used to be ignored in the past but these days I think you will find the Notary will ask the solicitors for each party that all taxes are up to date.

Knowing that Patsy lived here for a while, I assume that she was, and can still claim to be, resident.

This being the case, you won't have to pay the 3%.

Depends whether she was a fiscal resident i.e. paying her taxes in Spain

As patsywhitehair says she's about to pay her non resident's tax, I assumed she was non resident for the tax year in question! And she hasn't yet sold...