This is actually a magic trick that done by magicians. Someone fires a gun right at their face a they catch it with their teeth. If they did this legitimately or not is just questionable as any magic trick. Heck some have died doing this trick.
This probably wouldn't work despite the fact that tooth enamel is harder than steel. The root of the tooth would get torn off by the sheer momentum and the bullet would continue through the neck of the victim. I also doubt that Trixie has faster reflexes than a computer, unless she is Neo's unknown sister.
Actually according to my calculations, if Trixie was to catch the bullet in her mouth it would cause a reaction that would make both Trixie and Applejack explode. Trust me I did the math on my solid gold-silk covered calculator was designed by Intel, Microsoft, and Apple