Growing joints need a different limit
A puppy's enthusiasm is a poor guide to what her skeleton can handle. The growth plates at the ends of her long bones are still soft and closing, and the joints of a young dog, especially a larger breed, are more vulnerable to repetitive strain than an adult's finished frame. Family walks create a particular risk because the pace is set by human legs and human plans: a puppy trots to keep up, rarely chooses the distance and will keep going long past sensible tiredness to stay with her people. Shorter, slower outings with freedom to sniff and pause load her joints far more kindly than one long march at a steady adult pace, even when the total time outside looks similar.
The walk itself tells you first
During the walk, early signs of too much are easy to miss because they look like behaviour rather than tiredness. A puppy who starts pulling ahead may settle, but one who begins lagging, drifting to the side, sitting whenever you stop or lying down flat on the path is asking for the outing to end. Puppies who are overtired often get sillier rather than quieter, mouthing the lead, jumping at family members and losing the manners they had at the start. Treat those changes as the end point, carry her or turn for home, and make the next walk shorter than this one rather than testing whether she can manage the same distance on a better day.
Afterwards matters as much as during
The clearest evidence often appears later. A puppy who has done an appropriate amount comes home, drinks, and settles for a proper sleep. One who has overdone it may race around in a wired, frantic way and then crash heavily, or may be stiff when she gets up from her nap, reluctant to climb a step, or less keen on the next walk than usual. Keep a simple note of walk length, ground type and how she was that evening and the following morning for a couple of weeks, because patterns are much easier to spot on paper than in memory. That written pattern is genuinely useful information, not owner anxiety, and it turns a vague worry at the vet's into a clear picture of what her joints are coping with.
Build the day around sniffing, not distance
If family life involves a proper walk that she cannot yet match, split the difference kindly. On her own walks, choose soft, varied ground, let her set a wandering pace and build in stops where she simply sniffs and watches the world, because sniffing tires a puppy's brain without loading her joints. Avoid the hidden strain multipliers that add up across a day: repeated stairs, jumping off furniture or out of the car boot, slippery floors at a run and long games of stairs or steep-slope chasing with children. Several short, interesting outings almost always suit a growing puppy better than one expedition.
When to check with your vet, and what to bring
Contact your vet sooner rather than waiting for the next routine visit if your puppy limps and it does not resolve with a day or two of rest, if she repeatedly lags or refuses walks she previously enjoyed, if one leg looks or moves differently from the other, or if stiffness after ordinary walks becomes a regular pattern. Bring your notes on distances, surfaces and after-effects, along with her growth and weight history, so the vet can judge her exercise against her actual development rather than a generic rule. Keep those walk notes and visit records together in her KinsLe Pet Passport, the portable packet of her records that travels with her to vet checks, so every conversation about her joints starts from her real history.