Continuity mistake: When Buffy comes in to talk to her mum about the CAT scan, we hear her shut the door behind her. We then cut to a shot of Buffy, and can see the door slightly ajar in the background. (00:10:30)
Continuity mistake: When Joyce is talking to Buffy about the shadow, after she says "sometimes weeks", she turns towards Buffy. In the next shot she's facing away from her, then turns to face her again. (00:10:55)
Answer: She has superpowers, ergo fast movement. The reason she outruns him so easily in "Touched" is that she stops trying to actually fight him and just dodges instead.
Shay