You get 5 diamonds from this Sharing button and it refreshes every day.

There are two ways to Rank Up and get to this button. You can either get it in Stylist Arena or by doing a quest in Nikki’s Journey. You need to do them both manually. The easiest way is to go to the Stylist Arena, click Find Stylist and then Start. If you win you’re guaranteed to rank up. The other way is to do a quest manually in Nikki’s Journey. If you manage to get a higher rank than before you will get the Rank Up and be able to Share.