I think it goes a little deeper than "have and have not". The word "Decided" is bolded, and I think that's for an important reason now that I think about it.
Winslow could have asked for this chassis at any time, and Hanners would have likely said yes. He "Decided" that he wanted to be more humanoid, which to May may make it sound like a trivial whim. We have no idea what Anthro-PC jail is, but it probably involves having any form of physical form taken away from them. That means that to May, having even a dipsy little chibi form is a gift to be appreciated, and becoming a full sized humanoid with complete autonomy isn't something that should just be taken for granted.
Make no mistake, I feel her reaction is out of line, but I don't entirely blame her for it. This goes beyond material possession and kinda delves into the concept of liberty and freedom. I mean some serious "I have no mouth and I must scream" kinda shit. The idea of AnthroPC Prison kinda terrifies me on a new level. I'm getting thoughts of having your consciousness blocked off from all physical stimulus, and only having access to I dunno, the financial records of an accounting firm as my only form of stimulation. I'd say that'd be inhumane, but then again, we don't exactly know if 'humane' is applied to AIs.
Momo has spoken a lot about how it's been a struggle for AI's to get civil rights, and that from day one with the first AI has wanted to be treated as an sentient equal. So for Winslow to so casually get what others struggled for on a whim, rather than it be something he's wanted since day one? I can see how that can be a bit of an middle finger to both May and Momo, and most of AI kind.