My interpretation is slightly different to @ChristopherFritz’s, though I feel we reach about the same conclusion. I won’t say that I’m 100% sure about it either though.
あんなの
あんな means “that sort of, that kind of”. As mentioned before, the の is being used as a pronoun, something that is replacing a noun that is usually determined by context. I’ll come back to what noun should be here in just a moment.
The tricky part is the で that we have here. My interpretation is that this is the で particle. One of the uses of this particle is to denote a slight causal relationship. The dictionary of basic japanese grammar give this example:
山口さんは 病気 で 学校 を 休んだ。
Yamaguchi san ha, byouki de gakkou wo yasunda
Yamaguchi was sick, and absented himself from school => because Yamaguchi was sick, he was absent from school.
Going back to our current sentence and our hypothesis of a causal relationship for で, we have:
あんなの で 転ぶ
Because of that thing, (Kanami) fell over.
Well, what exactly made Kanami fall? This guy here has something to say about it:

Kanami fell because Sae pushed her. の in あんなの refers to that fact. Now, from where I see it, while Sae does mean-spiritedly push Kanami, she was just trying to lightly mess with her, not actually make her fall. Part of the problem was that Kanami had her mind elsewhere:

Sae’s just lightly pushes her from one shoulder. It’s not a full-on two-handed push sure to make her fall.

Sae’s face after they all fall like dominoes makes it kind of clear she didn’t expect such a disaster:

So basically my understanding is that
あんなの で 転ぶ => Falling over from from such (a light push)
Now, we just need to see how this connects to 方が悪い. I agree that this is comparing two things. One of them is bad, and another is not.
あんなの で 転ぶ 方が悪い => Rather, falling from (such a light push) is wrong / abnormal.
Rather than what? Rather than what Sae did. Sae’s basically saying, that rather than her being wrong for pushing Kanami, Kanami is wrong from falling from such light pushing. In other words, Sae is just trying to shift blame.









