If Smurfette has a heart above her head, tapping this means that she gives 15 XP for every Smurf who is close to her. This happens every couple of hours. With this patience is a virtue, because there should be as many Smurfs around her as possible. A good trick for that is to tap on the Smurfs at a specific area, once tapped they start waving with their hand and don’t move anymore. That way a lot of Smurfs can be gathered in that area and as soon as Smurfette comes nearby they will all give the extra XP. Another trick is to wait until a harvest is done, then all Smurfs stop working and start walking around, usually all at once, so it is easier to gather them in one place.
Smurfette will only give the bonus XP to the working Smurfs, the special Smurfs like Papa, Brainy, etc. are not affected, even if they are in her proximity.
If you don’t buy Smurfette, she will visit your village in some seasonal updates, i.e Christmas and Valentine updates. She will eventually give you some quests and riddles.
For Smurfette Valentine’s riddles visit Riddles page.