I don't think Trixie thought Evelyn was treacherous.
Remember all their personal meetings before "to Break a Thief", she always treated Evelyn with contempt (called her a "cow", "cow professor")just considering Le Fay a rich fool.
She just didn't like her, as a rich representative of the city's bohemians.
But most likely Nancy's investigation gave her food for thought, (plus it is unknown what she saw in the houses that she robbed) that's why suspicions arose.
But mind you, even going to the "case" in "to Catch a Thief", she still did underestimate the danger. So she didn't suspect.
No. Mind you, Evelyn is talking here: That Trixie just robbed rich ladies:
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No contracts.
Yeah. The last one who didn't die. Us, and the guys on reddit.
The freshest of the zombies.