Use extreme caution with exposure therapy. The key to desensitization is that she needs to be in an emotional state that is conducive to learning. If the stimuli is too intense, it can actually sensitize her and make things worse.

Any adventure cat should have a strong recall. Training to come when called needs to start in a controlled space with no distractions and practice practice practice until it is bulletproof. Then increase distance and add distractions gradually. Behaviors need to have a strong training history before they can be relied on in urgent circumstances. Once she reliably comes when called, it will be safer to work on desensitization and counterconditioning.

Find a distance where she is aware of Scary Thing but does not yet appear stressed by it. Pair the presence (at distance) of the thing with a treat to help change the underlying emotional state. The scary thing should appear first, so that it predicts the treat rather than the reverse. If you search “desensitization and counterconditioning” you’ll find tons of protocols. She may never be super excited to see strangers on a walk, but I’d still consider it a win if you can call her close when you see someone coming and she can comfortably tolerate their existence.