Right, I understand this. But in the accounts I've read, Guede has Meredith calling Amanda "that *advertiser censored* of a doper" and that "drugged up tart", and to me that doesn't sound like Meredith. Unless she was really furious...but I get the conjecture as to motive...
I know Guede described conflict between Meredith and Knox, conflict that was confirmed by family, friends and roommates. If Guede says that Meredith was upset that Knox was stoned as often as she ate pasta, then either Guede has remarkable insights into human nature, or he witnessed conflict between Knox and Meredith.
The alternative is that he imagined it and coincidentally it was true.