the reason i said i dont want to be isabelle is because i believe MAYBE this time traveller is the main villain. the MC it self try not to do the same things and do better (just for him or for people around him). he acts different from before. but this person changed things. what if isabelle had a bad future just like mc? if she became cruel enough to steal from her of the past to change things? i see happening, she has potencial for evil just like kate. we see that in the quest before lindsay.
I'm almost sure that Mer is neither a villain, nor Isabelle.
A villain wouldn't remind the MC that his choices have an impact on the ones around him; or get happy (+♥) if MC thanks her for this reminder; or praise the MC for standing up against Kate.
Isabelle wouldn't mention that
Flora hates the pre-loop MC, because pre-loop she stayed in the UK, so she wouldn't be acquainted with Flora. At most she'd say "
your sister hates you".
Another important detail against Mer being future!Isabelle is in the scene where the MC goes down on Mrs. L. Mrs. L asks her something like "What are you doing here? You never step in my classroom!". If however Mer was a future!Isabelle, Mrs. L wouldn't ask this, because she'd know that future!Isabelle is avoiding present!Isabelle. (That applies to
all students that you see in Mrs. L's class, by the way. So if Mer is a time-travelling student, she's either someone who didn't appear yet, or a future Maxine. It's up to debate if the MC would recognise the voice of a future Maxine.)
...or perhaps Mer = a future anthropomorphised Spinach‽‽‽ [broma]