but then what about 'a hull' being her apple, not his? (pardon the lack of accents)
It's because úll starts with a vowel, and portán with a consonant.
You should take a look to the Tips and notes of Possessives, it's clearly explained. I personnally read it when i'm confused.
The prefixed H in a húll isn’t an example of lenition; the leniting H always follows a consonant.