I have no vested interest in Roundup's success, and I have a civic
disinterest in just about anything Monsanto is saying. They have a track record of lying about the safety of the chemicals they produce. They're the DDT company, after all.
As for why I distrust this woman: see my original comment. She isn't an expert, and she has a reputation of publishing junk science. The preponderance of historical evidence is already against Monsanto, so the junk she peddles is just noise in an otherwise compelling argument that glyphosate needs more scrutiny.
Put another way: if I were more conspiratorially minded, I would see someone like Seneff as controlled opposition: she's just credentialed enough to ensnare otherwise well-informed lay-people, but also just enough of a crank to be trivially discredited by potentially dishonest actors. But I'm not, and I'm inclined to treat her as another in a long line of well-intentioned non-experts who actively diminish the credibility of glyphosate safety research.