Unfortunately, I know nothing about Portuguese inheritance law. But let's assume for one minute that Portuguese law will follow UK law (as some european jurisdictions do when the testatrix is not ordinarily resident in that country). I assume your friend is ordinarily resident here.
I would suggest that she makes a Portuguese Will which leaves the entirety of the portuguese property to the daughter. If she is unable to do that I would suggest that the daughter does NOT pay rent (this will mean that if it comes to a claim under the Inheritance (Provision for Family and Dependants) Act 1975, the daughter has a better "needs" based defence.
Had she got a bit longer, I'd suggest transferring the property into daughter's name but you really need to do that more than 6 years prior to death to prevent it being "clawed" back under the anti avoidance provisions under that Act. She *could* transfer it to her absolutely now and write in the Deed that it is in consequence of her natural love and affection for her daughter and to ensure that the business she intends to run has a sound basis. that *might* work under anti avoidance provisions.
I didn't see the original thread otherwise I would have corrected one or two points. The son can make a claim on the estate under the above act whether or not he was dependent – all he needs to be is a son. I accept that the more independent the two are, the weaker the claim, but if you look at cases like Illot v Mitson (where an estranged daughter still got an award) nothing is set in stone. Whilst the testatrix can, as has been suggested, leave a side note saying why she does not wish her son to inherit (this can be taken into account by the Court), such letters are seen as a little self serving.
I do think the key to this could be some very well drafted attendance notes by a solicitor. They will always be considered by the Court.
It was suggested on the other thread that she should use an “in terrorem” clause (ie, I leave him x, but if he contests the Will he gets nothing). As was properly pointed out by Tony, unless a significant sum is left, this is unlikely to be worth doing. The difficulty is, IF she leaves him a sum, this may lead the Court to form the view that she felt under a moral obligation to do so (which broadly relates to one of the factors under the Act).
I think the best she can do is see a solicitor (preferably a member of the Probate Section of the Law Society or a STEP member) and get all her affairs in order. To look on the bright side, if the son has no money he won’t be able to afford a lawyer to take this on and given the legal aid cuts is unlikely to get Legal Aid. I doubt he would be able to afford a premium for After the event insurance either.