Nose picker
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Our biggest concern with this particular battle is first making sure she doesn't eat it. We do tell her picking her nose is yucky, but she has spent two years having us picking and wiping and sucking boogers out of her nose so it's confusing for her why she can't.
I still pick my nose lol it's very satisfying lol
Educate her about germs and talk about how she's been sick before and didn't like it, if she eats her boogers, she'll get sick more and (insert sick symptoms she hates). Then have tissues available where she usually picks. And maybe have something desirable to do afterwards, like hand sanitizer or washing her hands in the sink (playing in water is great fun, being tall on the bathroom stool is awesome)
Or you could have a sticker chart for each time/day she picks and doesn't eat with a prize after a certain amount of time
Tell her it is private and to do it in the bathroom with tp or a tissue. Teach her how to blow her nose instead? Tell her to squeeze her nose for itches. I distracted my son from his nose with toys. I told him it was icky and to not do it, then moved on to something else. Don't make too big a deal out of it. Over time, I had some silly fun with my son, being goofy about picking his nose and saying it was eww yucky. Just like sucking their thumb, I alternate between serious talk, reasons why, something to do instead, ignoring it, and small reminders.