I do not think that Dr. Shumway is Xaafuun in disguise. She would be away to long from Izadora and she would have had to come out of the UFO when she was in another city. I do think that Dr. Shumway is the queen alien though. I find it suspicious that a scientist would jump to such conclusions with:
1. Not stating any evidence
2. Not even investigating
3. When the subject comes up, Dr. Shumway shoos it away by calling it nonsense.