Unfortunately, I don't know that much about heart rate, and I am unable to download all of her data to analyze it, but her heart rate seems to be quite low in the second half relative to her own heart rate in the first half. Again, it may be due to inaccurate measuring by the watch, or perhaps she naturally has a low heart rate late in races, or maybe lots of people do, but again, she had one of the most incredible performances ever in the final climb, so my guess would be that her heart rate would be significantly higher in the final miles.
For example, and note these are random times, but at 6:07:41 in the race she was running a pace of 10:03/mi and her heart rate was recorded at 147bpm while she was at sea level at the temperature was recorded on her watch at around 90F.
At 15:53:04 she was running a pace of 9:37/mi and her heart rate was 111bpm while at an elevation of 4,995 (almost a mile above sea level) and her watch recorded a temperature of 100.4F.
Again, I am in no way saying this is an illustrative example, but 10 hours later in the race, with the temperature 10 degrees hotter, and the elevation 5,000 ft higher her heart rate was 36bpm lower.
Although those are just two random points, it does appear that starting at around hour 15 her heartrate averages around ~20bpm lower for the rest of the race than it was in the beginning. [The first file on her watch for the first 20hrs has an average of 130bpm, and the last 4 hours including the climb up Mt. Whitney has an average of 118bpm (although as mentioned there appears to be a noticeable decrease in heartrate around hour 15.)
It is really sad that people cheat in running races and ultras and similar rather noncompetitive events, and although I don't know whether or not Ashley Paulson cheated, I appreciate that she shared her data, and I hope some more knowledgeable people are able to fairly analyze it.