Couple of things are coming to my mind you may want to check/try
She wears specs anyway is she needing an improved prescription?
Has she been checked for colour blindness? It can present differently in girls sometimes and can be harder to spot. Plus children's books tend not to be black print on white background and the varying colours used can make it harder for colour blind kids to learn to read
If she's missed a lot of school she may well be subconscious about reading aloud especially with a speech delay. If she finds expressing words easier in song let her sing a book to you? Might help her break a barrier
Find books, comics, postcards whatever with words on that appeal to her musical interests. Reading things that interest us is half the battle.
The hearing thing may be an over sensitivity to sound which can mean certain words sound different to her than to you or I, I don't profess to be an expert in this area this would need SALT input and probably quite specialised too
Hope you find something that helps but I agree don't punish her for her interest in music. It's a great talent to have and really helps with lots of other learning
Her health issues may appear unrelated but the missing school element plus possibly the lack of development of neural pathways etc as a result of her body focusing on healing the ailing organs will have has an effect
I'd need to know which organs and the specific condition to know the likely effects or more likely a health and education specialist would need to, paediatrics isn't my area, but it's surprising how certain seemingly disconnected body systems can impact each other