I always went along with Riso and Hudson's typing of her as a 5w4, but her social media pleas for help made me question it. Wouldn't unhealthy Fives (esp. with a four wing) become intentionally isolated and minimalist, seeming outwardly ....reserved I suppose?
I'm not sure. I can't give a confident answer without thinking about this for a while. My immediate reaction was that she was more likely a 4x5 than a 5x4. I'm not familiar enough with every enneagram to suggest different combinations.
She is often typed as an INFP. When INFP is matched with 4x5, though, her hard edges and politics dissolve.
Singer Aurora is the best example of a performer who is INFP, IMO. She and Sinead seem nothing alike. While I know typing is about cognitive function and not outward behavior, we must also consider that songwriting is an emotional art by default, and most types are more emotional when producing this kind of art than they would possibly be when they step away from the craft. (Anger is an emotion, too, so this includes angry music.)
She was also bipolar, which would influence her behaviors and possibly lead to mistyping. A trait of BPD is poor emotional regulation, for example, which would make her appear more emotional than her possible true type -- either in Enneagram or MBTI.
Maybe people who study the Enneagram system more extensively or have a different type will weigh in.
Finally, per my joke post above, I can verify that 5x4s intentionally isolate.