I think it makes perfect sense. Like I said before I don't for one second believe that the will states that she has to be nice to the MC, rather that she needs to manipulate the MC. After all it's hard to manipulate someone who doesn't like you.
That would make zero sense seeing as the MC's conditions are to avoid Monica and the girls anyway.
Why would a supposedly intelligent man give the woman conditions that could possibly mean less than nothing if his son carried out the ones given to him?
He wouldn't, it's silly. It would instantly grant Elaine her part of the money without doing anything.
Elaine wasn't the one that said his dad made her act cruel to him, his dad said that himself. Hiw own words in the recording, he forced Elaine to treat him like shit.
Lets also consider that Monica has told a soon to be rich MC all about her financial problems. An MC she hasn't seen for years.
It's okay to dislike Elaine but Monica is also shady as fuck.
P.S. There is also the e-mail that only Monica seems to have any knowledge of. An e-mail sent from a cyber cafe now coffee shop near where Monica lives and sent by someone that looks like Monica.
Lets also consider the fact that in order for Elaine to be able to drive a wedge between the MC and anyone it would require the MC to not only forgive Elaine but be on friendly enough terms with her to accept anything she says about people he knew and had good memories of as a child. It's too much of a wild card for, again, a supposedly intelligent man to have as a condition. It would be too much of a long shot for him to consider worthwhile.