Is she living alone? If so, she can form a bubble with one family. If she chooses her parents and is in no other bubble that's fine.
Which country of UK (in Wales can only travel 5 miles)
In England, where a person lives on their own (or solely with children under 18 years of age) that person can choose to 'link' with ONE other household (of any size), to create a 'social bubble' as long as:
(a) the person living on their own (or with children) hasn't already 'linked' to any other household ;
(b) the household that they plan to 'link' to isn't already linked to any other household ; and
(c) every adult in the second household consents to the 'linking'.
So if the daughter in your question lives alone (or with children) she can 'link' to her parents household as long as she hasn't already got any other such 'link' and neither have they. She can then meet her parents indoors.
If the daughter lives with other adults (or if there are any pre-existing 'links' barring the creation of one between her own household and that of her parents) she can only meet with her parents outdoors.
Yes, as long as you stay out of doors - apart from visiting the loo and, as we found, taking the dog inside to have a drink. Going in and hugging etc. would mean you had to be in her 'bubble' (hate the word already).
It'll have to be a meeting outdoors then, Bazile, observing the 2 metre rule.. (It's permissible to pass through a house to get to a garden or to nip into the house to use the loo though).
There's some really good weather forecast for much of the country in the coming week, so that would be a good time for such a visit.