Why cyclists are harder than they look
A bicycle approaches almost silently from behind, moves fast, and presents a narrow, wobbling, fleeing shape, which is a near-perfect trigger for a dog's chase instinct. The cyclist often reacts too, wobbling or speeding up, and both responses make the target more exciting. Herding breeds may try to round a bike up rather than catch it, while nervous dogs lunge because a fast object has invaded their space, but from the saddle both look and feel the same. A chase or a snapped lead can injure the rider, your dog, or both, and in many places allowing a dog to worry a cyclist brings legal trouble as well. Treat this as a safety behaviour to rebuild carefully, not a quirk to shout down on the towpath.
Distance is your training tool
Every dog has a distance at which she can see a cyclist, feel the pull, and still choose to look at you and take a reward. Training happens at that distance and wider, never inside it. Start somewhere you can watch a cycle route from well back, such as across a field from a path, and reward every orientation toward a bike followed by a look back at you. If she fixates, stops responding or starts to whine and strain, you are too close; increase the gap without drama and work there instead. On narrow paths, create distance actively by crossing the road early, stepping into a gateway or turning down a side turning before the bike reaches you, rather than pinning her against a hedge as it squeezes past.
Stage the cyclist instead of ambushing strangers
Real cyclists on a shared path are uncontrolled, fast and understandably unwilling to be training props. Recruit a friend with a bike instead. Have them ride past at your chosen distance, slowly at first, while you reward her look-backs, then vary the speed, direction and closeness across sessions as she succeeds. Practise the surprise version too: a bike appearing from behind is her hardest case, so have your helper approach from behind at distance, call out early so she is not startled, and pay her well for turning to you. Keep sessions short and end on a success, because rehearsing calm responses in small doses is what gradually changes what a bicycle predicts for her.
Handling and habits on shared routes
Use a lead short enough to prevent a lunge reaching the path, attached to a harness that will not hurt her neck if she does launch, and keep your attention ahead and behind on cycle routes rather than on your phone. Teach a solid watch-me cue and a hand touch she can perform when excited, giving her a familiar job in the moment a bike appears. Do not let her off lead on shared-use paths until her response to bikes is reliably bored at close range in staged practice, and even then choose places with clear sightlines. If she has already made contact with a cyclist, or her lunging comes with hard staring and silence rather than excited noise, get a qualified behaviour professional involved and discuss the pattern with your veterinarian.
One plan for everyone who walks her near bikes
Progress evaporates if a weekend walker lets her practise lunging on the canal path while you train carefully all week. Share the specifics: her current safe distance, the look-back game, the routes to avoid for now, and the rule about off-lead freedom on shared paths. In KinsLe, Care Teams lets you put that bike plan inside her walking duty and log each staged practice session as completed, so whoever takes her out knows exactly how close a cyclist is allowed to get.