Or we could surmise that Trixie was doing it to save her ego and image. I like Trixie, but I think it's intentional she's supposed to be an egotistical jerk within the canon. I think your right that she wouldn't have started anything if the mane crew hadn't been butting in as usual.
I think I saw four different Trixies.
- Show persona (a fundamental part of her act)
- Improvised show persona (after Rarity/AJ/Dash disrupted her show)
- Tired of performing but still trying to keep up the act (when kids wouldn't leave her alone)
- Real Trixie (in a crisis)
- Improvised show persona again (when making her exit)
I think Real Trixie was being genuine. I don't think you could make her fight a monster just to save her image. The "Trixie" everyone hates would've just ran away and disappeared, and made up a story to cover it afterwards. She
knew the monster was undefeatable
and was already running scared. I think Trixie did what little she could because she could, while having difficulty trying to explain "an act" to children.
And I don't expect the official canon to do Trixie any favors. Amy Keating Rogers (the new head writer for S3 onward) said in an interview that if Trixie comes back to apologize for what she did, the mane cast would obviously forgive her and she'll be accepted as a good pony, but if she comes back to start shit like last time, she'll stay a villain. AKR apparently doesn't believe Trixie has depth.
I'm gonna have to stick with my headcanon for now. Trixie didn't start shit. Rarity and AJ did. Trixie doesn't need their acceptance.