It is important to understand the change in English teaching in the UK in the 1960s which meant that children were no longer taught the structure of the language. From then on understanding of usage was gained passively. This meant that the next generation of teachers did not know the correct use of English and this has had a knock-on effect over the intervening years. Reading internet posts shows the low level of literacy in English.
I have found that those who use English best are the people who learned it as a second language and were taught the rules formally.

It would be "the doctor's woods" for one medic and "the doctors' woods" if there were more than one.
So, given that Heaven is singular, it is "Walking Heaven's woods with her daddy."