Not all English dialects distinguish between the HAPPY vowel [i] and the FLEECE vowel [iː]; for example, General American does not.
One distinction that is made in all English dialects is the tense/lax distinction: the FLEECE vowel, tense [iː] vs the KIT vowel, lax [ɪ].
Note the terminology of tense vs lax, not long vs short. This is not just a length distinction, but a quality distinction. The tense vowel tends to be longer, higher, and sometimes becomes diphthongized.
EDIT: I realized I only answered part of your question.
She's < she is and she's < she has are homophones in all dialects. There is no difference in pronunciation based on the meaning of the contraction.
I do understand how attributive and predicative adjectives work, yet I can't find an easier way for learners to differentiate between both types - especially if such differentiation doesn't exist in their mother tongues.
I'd like to suggest that maybe a reference grammar might be able to help you here. For instance, the 2002 reference grammar by Huddleston and Pullum et al., The Cambridge Grammar of the English Language (CGEL), discusses this very issue: "Chapter 6 Adjectives and adverbs", part "4 Restricted function for adjectives", on pages 553-562.
CGEL, in "4.1 Attributive-only adjectives",
- Adjectives that do not normally occur except as (heads of) attributive modifiers include:
which includes an example list of 30 adjectives (e.g. drunken, future, mere, putative, umpteenth). In this part, they also discuss "Meaning differences between attributive and non-attributive uses".
They also discuss "Potential differences between attributive-only and ordinary attributive adjectives"; where they discuss the four properties that ascriptive attributive adjectives characteristically have, but most attributive-only adjectives lack one or more of them. The properties are: entailment, subset, modifiability, pro-form.
Then they go on and discuss "Some types of attributive-only adjectives". In this part, they say:
- Attributive-only adjectives are too numerous and semantically heterogeneous to permit a simple and exhaustive classification. Instead we will here illustrate and comment on some of the most important semantic types.
Some of those types are: degree and quantifying attributives, temporal and locational attributives, associative attributives, process-oriented attributives, modal attributives, particularizing attributives, expressive attributives, hypallage: transferred attributives.
CGEL, in "4.2 Never-attributive adjectives", discusses "Adjectives which can occur predicatively or postpositively, but not attributively". These include "Adjectives formed with the 'a' prefix", and provide an example list of 24 adjectives (e.g. afloat, aglitter, alike, averse).
Also, includes "Adjectives with complements". And also includes "A small set of other adjectives".
And then includes "Postpositive-only adjectives", which are described as:
- A handful of adjectives are restricted to postpositive function:
and they provide an example list of 6 adjectives (e.g. flowers galore, the President elect).
Okayee, my fingers are tired. Hopefully I haven't made too many typos. It seems to me that CGEL has a lot of good info in those pages that might help you out (pages 553-562).
Best Answer
Nearly all the dictionaries only give /ˈkɜːrsɪd/ as a pronunciation associated with the metaphorical usage.
Oxford Dictionaries Online lists both pronunciations, but only gives the meaning
Cambridge Dictionary does the same thing:
As does the American Heritage Dictionary:
The first two of these specify that cursed is an attributive adjective.
Collins Dictionary specifically notes that the pronunciation /kɜːʳsɪd/ is associated with sense (3):
This leaves Merriam-Webster as the one dictionary that gives both pronunciations, both meanings, and no usage guidance.
So on the whole, the dictionaries agree that the two-syllable pronunciation should only be used for the metaphorical meaning.
Do people actually use the /ˈkɜːrsɪd/ pronunciation only for this meaning? I suspect many do. I also suspect many people don't use this pronunciation at all, and for some of these people, /ˈkɜːrsɪd/ sounds like a pronunciation with an old-fashioned feel which might seem appropriate for Harry Potter, for either meanings.
Which meaning was intended by the writers of the play? Since I haven't read it, I can't say. But maybe both.