My theories...
I don't think whomever killed her planned it out in advance, eg I don't suspect poisoning but more like an aggressive act in the heat of the moment. UNLESS it was someone who wasn't part of the family, e.g. a mistress, then that person might have less care for her. I don't think anyone who was part of her extended family would have that level of callousness. I might be wrong, but that's not what I'm thinking happened.
I don't think Allison suicided. The police are treating it as a homicide for one and if she was going to suicide why would she get her hair done, leave her house at Brookfield without her car, and somehow get to the Kolo overpass which would be a very long way on footand do it somewhere there? Makes no sense to me.