Although the first picture shows some what of a larger nose than what she appears to have now, I wasn't really convinced. A lot of younger girls may "grow into" their noses as they get older and as their face thins out or whatever.
Earlier today, people were back at saying she had gotten a nose job again. At first, I didn't really pay attention to the rumors until I watched the new vlog she uploaded today. She looked different. She added an annotation into the beginning of her video saying she had done her eyebrows differently; probably to add some excuse to her different appearance. It's also apparent that she's hasn't done a video in awhile; the last one she did was about her Miranda Cosgrove meetup, which was filmed weeks ago. She also stated in her video that she had a good reason for being absent for so long, but "its probably not worth anything", so we never actually heard it.
Her nose is looking rather Micheal Jackson-ish, no?
Notice how in the "before" picture, the bridge appears wider and the tip not as refined and turned up as the "after" picture looks..
I don't know wtf she did to her brows, either, but she kind of has that perma-surprised look on her face.
Now, it isn't definite that Blair had a nose job, I doubt we'll ever know one way or another, I'm sure when asked, she'll deny anything having to do with a nose job. But based on these pictures, you can decide for yourself :) Ahh Lizzy, keepin' it real!