There it is! They're too young.

It is called Melanonychia, which runs from under the nail bed through to the tip vertically. It is an excess of melanin in the nail and _could_ be just that however you are 100% correct in stating it could signal something much more serious. Sometimes it may be a thin brown line & others a very dark or black thick line. Regardless, you must always get it checked out! It can range from certain deficiencies, a sign of HIV or even one of the most aggressive cancers which is Malignant Melanoma. Though we do not know if this person has had it checked out or not and maybe even it is just excess melanin deposits that they've had most of their life, it is always good to make people aware of something, an anomaly, that we may spot in a video as it could save someone's life. Someone else's health is always extremely hard to approach but in some cases, such as this, it is a learning moment for so many in the comments who are just scrolling by. The more you know. 😊

If you live in a country with a Decathlon store, you can maybe get roller skates for 40 euros. But make sure to check their website b4 driving there

Go to a secondhand shop, you will find some, that girl needs her skates