The last thing I would want is for "peer pressure" to "take care" of my child's bad habit. Send your child to school with any bad habit, and schildren remember it all the way through high school. And children today are meaner and meaner than they used to be.
All three of my children pick their noses, but if I try to clean them out (q-tips, saline, anything) they're furious with me. What I have finally started doing is explaining WHY they have boogers. Hairs in the nose catch the germs that, if inside our bodies, would make us sick. With my older children, I gave a little more info-
Anyway, it has started to take hold with my 4 and five year old, and Ive found them less and less picking their noses. My two year old still pretty much walks around with his finger in his nose.
While I have always believed that there are two types of people in this world; those who pick their noses and those who lie about it, all you can really do is teach her- and sometimes it takes many many lessons explained in different ways. I doubt your daughter is old enough to understand why its yucky or that she should wipe it in a tissue.
At 19months, this is one of the few things that she can see with her eyes that comes from her body- so if she understand that poopy, pee, and ear wax are yucky, group boogers in the same category for her.
Until she can understand though, all you can do is behavior modification- trying to get her booger placed somewhere other than her mouth by her.
As with most things with children, time, time, time... everything takes us time...