You can jog/run a marathon at any speed, it's not a sprint, you can jog at a brisk walking pace - a speed of 6-7km per hour for example, and still qualify as jogging/running a marathon or half marathon. Based on all the info in this thread and everyone's examples of 7km turn around time variance and return (14km total), the fact that Mount Clear indicates elevation in its name as well as the sleuths that have posted terrain maps of the area she was running, we know the whole track has changing terrain and elevation, it's totally plausible it took her close to an hour especially if she was jogging at a slow pace to train for her marathon which a lot of people do do, I don't think she was hoping to be first place.
Although there is room for speculation and I think it may be wise to refrain from trying to assume Sam's definite running/jogging speed outside what LE have advised, or what she set out to achieve that day, we simply don't know that information and we have to remember the old saying "when you assume, you can also assume your wrong", LE have advised the time frame we have which makes complete logical sense if she was jogging a slow speed.
Another thing to consider is she had been out to dinner the night before, we all know how alcohol affects the body as we age, if she had a few drinks and or didn't get an early night she might of been sluggish that day, she also could have been taking it easy due to a recovering injury we are unaware of or just the break from running/jogging she may have had after her bout of Cov.
Appreciate the theory nonetheless that someone else walked her route to make it seems as if it was her, we won't know for sure until and if LE make this information known to the public, but for the time being LE have advised that something happened once she made it to Mount Clear her supposed turn around point, they have enough evidence to arrest PS for Murder, and that her life ended at that turn around point by his hands, they don't do this lightly without solid proof and evidence.