Yo, I found yet another female AR (Thank heavens for advanced Google searching, that feature is fucking awesome), this time in a manga called
Hakui-san to Robo.
It seems to be a new slice-of-life manga published in the magazine Manga Life, detailing the lives of schoolgirl Hakui and her robot. I haven't found a more detailed summary so I can't say much more. ^^" In one of its chapters, published in the magazine's August 2017 issue, Hakui is transformed into a baby by eating a red candy; an obvious reference to good ol' Marvelous Melmo. Robo has to take care of her, and hilarity ensues.
The chapter hasn't been released in volume format yet, but thankfully, there are extracts from the chapter on the author's official Pixiv page. There doesn't seem to be any process, as the chapter seems to start with Robo finding Hakui already regressed, but it does show her in adorably oversized clothes. I'm eager to find out the rest of that chapter someday, as well as the manga in general; both look really cute!
https://www.pixiv.net/member_illust....st_id=63559410
And here's the page where I found out about the AR in the first place:
https://blogs.yahoo.co.jp/nama_k1/65943650.html
EDIT: The cover in the attachments is from volume 1, which doesn't feature this chapter, but I uploaded it for reference's sake.