it sounds like future MIL may be attempting to sway op away from obtaining legal counsel. That, to me, makes it all the more important that op does obtain her own legal counsel.
As to the actual question; There is caselaw that does ruled the lopsided financial status, alone, was not adequate to render the agreement void.
As well a lack of full disclosure of the husbandís assets was not adequate to render the agreement void
As well, the lack of consulting counsel was not adequate to render the agreement void although there was discussion regarding the fact the wife did have the opportunity to seek counsel. That suggests that a party not having adequate opportunity to seek counsel might provide for a different outcome.