I think an important distinction is that her position focuses on the intrinsic nature of pleasure and pain as feelings, not any relationship they have either to some even more fundamental concept of “objective value” or to our judgements, thoughts, and desires. We know pleasure feels good in the same way we know what the redness of red is like. Defining pleasure in terms of behaviors, beliefs, or desires can’t capture this in the same way that the wavelength of red light doesn’t convey the experience of seeing red. The power of this argument comes from taking this direct concept of phenomenal goodness (“feels good”) and inflating it into a full fledged account of moral goodness (hedonic utilitarianism).
Put another way: If we started out with no language for normativity, we wouldn’t be able to describe pleasure and pain without inventing one. (Try it!).
So pleasure has a “what we should value” property in the sense that “should” is already defined in terms of pleasure. But at a more basic level, value just is pleasure in the way water just is H2O.
Since moral knowledge in this view is just a special kind of descriptive knowledge the subjective position seems to flow from the objective one in a relatively straightforward way.
This argument is a bit circular, but I think that’s hard to avoid in general re: qualia. Of course discussion of qualia in your OP is relevant.
Speaking generally, it does seem like EA critics often equivocate between these two positions. For example, saying EA is bad for diverting money from soup kitchens to bednets but not being willing to say money should be diverted the other way. IMO focus on philosophical issues like utilitarianism can have the effect of equivocating further by implying more specific disagreements without really defending them.
(I don’t have any opinions about this book in particular).