Welcome to icliniq.com.
I have seen the pictures (attachment removed to protect patient identity).
This is mostly a wart. Melanoma is generally black in color and is very rarely seen in young age. This lesion of hers has mostly no feature of melanoma. Wart occurs due to one of these reasons say pricking, thorn or from other people if the virus gets into your skin. The virus stays there and slowly grows.
Also, a wart is infectious, i.e., after touching a wart if you touch anywhere else, you can get a wart there too. So the most important advice is "do not touch at all." Wart has to be removed as early as possible before it spreads much. It can be removed by radio frequency cautery which burns the wart and is removed.
Many creams and acids are also there to use, but I consider cautery as the first line of treatment, as chances of recurrence are less with it and the wart is removed in one sitting. I advise her to get it removed by cautery as early as possible.