you're right. i have a feeling that she would probably put him in the grinder.
another theory i have is that since the people making the series want to outstretch the war as much as possible they could possibly team up to kill simon.
she would try to kill negan but negan wont die. the war has to end in a final confrontation between rick and negan. also this new storyline will lead to the typical comic book route sooner or later.