Metal stuff needs a certain material/shader to allow transparency, SpcEnvAlpha_W. Here’s a partial list of shaders and their attributes:
Make sure her sleeve-bottom has a similarly transparency-compatible material/shader. The easiest way is probably to copy it from the top of her sleeve.
If you’re just trying to make things invisible, it’s usually better/easier to toggle the whole thing to ‘off’ in the asset explorer than to toil with alpha transparency. The only time this isn’t true is when you need some of the model to still be visible, and even then, it may make sense.
AO is only an issue with shadows, not with transparency.