I will preface this by saying that I am a Swiftie. I was when I was younger and am grateful for her music and general existence in pop culture because it has been such a cool bonding experience with my kids.
I don't think she snubbed Celine, I think she was excited (and probably tipsy). I'm sure she cringed when she realized. Lana writes for a lot of people who constantly win awards, including a collaboration on Midnights, but she never wins, so I get why TS wanted to bring her to the stage and recognize her. BUT, Lana clearly said no and didn't want to go onstage and TS did not read those cues at all.
As far as her acting surprised, how else should she act? Like she knows she'll win? Nonchalant? Then people would pick her apart for that.
She just at a point where people scrutinize everything she does and that's the nature of the beast I guess.
I'm glad SZA and Miley won!