Episode Discussion | Doctor Who | 1x08 "Empire of Death"
Logline
The Doctor has lost, his ageless enemy reigns supreme, and a shadow is falling over creation. Nothing can stop the devastation … except, perhaps, one woman.
I liked it but I'm finding the answers to a lot of the mysteries unsatisfying and I feel somewhat deflated. Why the snow? Why the song? Doesn't make sense if her parents are just humans
My interpretation is that it's mostly the idea that they believed that the incident was so important, it started to "bleed" into Ruby's present in times of emotional distress.
If we want a stronger explanation than that, you could argue that that point in spacetime was probably weakened by the presence of the TARDIS and Sutekh at nearly full-strength, plus whatever weirdness was caused by the use of the time window to view those events, and the creation of the Memory TARDIS.
That still doesn't answer why Sutekh couldn't just see her mother like all the other 7 billion humans on earth. Why her and not the other 6.9 billion people out there? It being random is just bad storytelling imo