She's still married to him. If he loses the election and the Republican party turns against him, and if he ends up having to pay half a billion in damages from his court cases, she'll run to the media with some sob story about how she felt she couldn't leave him sooner.
That's why he got shot. She's released from an NDA when he dies. Did she look concerned or upset that day or was she smiling just before the trigger was pulled? Did she have a "special" relationship with a few of the Secret Service guys? I really wonder.
Another poster had an interesting take today; She could have left him at any point and still be fucking a real billionaire while cruising the med in his super yacht.