Avril was interviewed by former Spice Girl Geri Halliwell at the Prince's Trust concert, and was asked what she thinks of Britney. Avril stated " I like her and I think she's hot".
We see that Avril doesn't hate britney at all, she likes her and her music (she got her album at home) but hates her sexy image.
That explains Avril's changing relation to Britney.
Credit: "BritneyTheBest12" from WOB forums.
Source: E-talk Daily.