I like your theories but I would personally tweak them a bit.
I think the ORIGINAL Mildred made the wish and gave up her life for her daughters/in sheer desperation to get out of that place and the "new" Mildred is the soul from 21st century.
With the baron I'm so with you on the magician or he had fairy blood from long ago. And all the bad endings is 100% him getting rid of people using money and magic/fairy power.
The spoiler I read
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The fairy godmother is the baron's mother or grandmother. That is why he has magic (and blew up his own house). I'm sure at this point we know that Ashley is not Cinderella.. it's someone else.
The only condition to make a wish to the fairy (which OG Mildred did) is to be utterly despaired.. then our Mildred came into this body.

One of the theories I have for this story is that Mildred met with one of the fairies and made a wish. What I don't understand is the she seem to have forgotten about that encountered.
Another theory is that the baron also met a fairy and made a wish and that could explain why people that go against him have a bad end. Or he could be a magician and that is one of the reasons he isn't married.