As others have said I can't see it being repressed memories due to the lack of aging of "not" Mihoko whilst the focus on the TV sets indicates quite some time difference.
Also "not" Mihoko says "I've never lived in that place" but yet the house on page 7 where she wakes herself up shouting Kinuko's name looks like the same house as shown on page 1 when she is Mihoko (though shown from a slightly different angle).
It would be good for a follow up to make things a little clearer - as trying work out what's going on makes my head hurt!