It’s because they are worn down. The base of your teeth are thick too- the bladelike portion is only the top half of what protrudes beyond the gums- the part she wore off.
Eating stone ground grain & dried meat, gnawing on bones, chewing hides, running plant fibers over the teeth to make the fibers pliable for basketry or weaving, using your teeth as pliers, etc, will wear teeth down.
If she had had an overbite they might not have worn down as far but she probably had perfectly matched jawsets that wear on each other, too.
When collecting sinew in the butchering process they probably ran it through their teeth to clean it prior to drying it, in the process scraping off fresh raw meat to eat.
Then they’d hang it up to dry.
When sewing with dried sinew, you put the sinew in your mouth to soften it with saliva; then you can use your teeth to separate it into threads and smooth it by pulling it over your teeth..
In that cool climate they doubtless made a lot of clothing and shoes using sinew as thread.