Why did I think it was her?

When I passed the fifth night, I wondered: "Why is Post-Mortem not available to us during the fifth and sixth nights?". I tried to figure it out and this thought came up and I have 2 reasons to think so:

• MOTHER's speech after the fourth night

• After jumpscares

MOTHER's speech after the fourth night

I decided to see what MOTHER says after burning the Hourglass, and I noticed these words: "You people shouldn't have come here, I shouldn't have let you. <...> I was wrong to let you pollute this place, to walk all over me, as long as I did". Yes, she may have been referring to the "Island of Discovery" itself, but it may also mean that she allowed us to this place until the fifth night.

After jumpscares

If you've forgotten what happens before 6:00, then I'll remind you: MOTHER kills us and we end up in a Post-Mortem. But when we go too far, the MOTHER (in an non-physical form) can also kill when we don't erase the drawing in the notebook, and this is what happens now: the MOTHER also kills us, but we are not given a second chance, because she does not allow us to get there. Also, with phrases in physical form, the MOTHER reminds us of what we have done and who she wants to kill us for.

Why is she giving us a second chance?

I can assume that she wants us to leave this island and not bother her and her "children", so she's giving us a chance to leave. But when we go too far, we make her angry, and she wants to avenge them, so we have to survive with one try. It is also possible that she controls almost everything and everyone, only some do not obey her (a good example is the Face). So, five characters combine into one.

I want to remind you that this is just a theory/guess and should not be taken as an objective source.