I don't find her credible or particularly caring. Certainly not very caring over her role in the arrest of PL.
On digestion issue...I am not an expert.
First, there is considerable normal variability among healthy people and animals in transit times through different sections of the gatrointestinal tract. Second, the time required for material to move through the digestive tube is significantly affected by the composition of the meal. Finally, transit time is influenced by such factors as psychological stress and even gender and reproductive status.
Several techniques have been used to measure transit times in humans and animals. Not surprisingly, differing estimates have been reported depending on the technique used and the population of subjects being evaluated.
http://www.vivo.colostate.edu/hbooks/pathphys/digestion/basics/transit.html
Based on that... I'm not hanging my hat on it.
From the link you just posted - the estimate from studies of GI transit indicate
50% of stomach contents emptied in 2.5 to 3 hours
This would seem to suggest that as Meredith had a full stomach (nothing had passed to her duodenum) an early time of death is far more likely. Perhaps her meal had a highly unusual composition(even though it was pizza), perhaps she was a one-in-a-million medical wonder (although no gastric pathology was noted at autopsy) - however, the most likely time of death would be early and it becomes more and more unlikely the closer you get to 10pm - and it becomes increasingly impossible the later you consider after 10pm. This should at least suggest reasonable doubt