Tomoko: If the TV’s on in the morning for no reason, I’m watching Anime (which is a catchall word for cartoons, on Japan-TL note)
Rainbow Dash: I’m Rainbow Dash!
Tomoko: It’s her (Blue Fast’s) fault I’m watching this ‘til the very end! She’s the baddest pone in the city!
(Note : Tomoko’s VA is the same as Rainbow Dash in the japanese dub)
The second sentence isn’t complete, and it makes no mention of Rainbow Dash (the comment to the side is separate). The せいで structure isn’t always literally blaming a particular actor, she’s just saying “because I unintentionally ended up watching it till the end…”, with the implied conclusion being “I had to run to get to school on time”.
Now the が悪い structure in the side comment isn’t used literally to say RD is bad (let alone “the baddest”), and this one actually does assign blame. The translator also seems to have confused 全部 (all) with 全都 (the entire city). The sentence simply says “It’s all that horse’s fault!” Hope this helps.
I don’t know what to believe anymore.