Yuck, that's pretty gross. I'm not sure it's in the "must move now!" category of offense, but you definitely want to deal with it.
First, I'd make sure you explained to her exactly why this is not acceptable, because she sounds kind of dense on the subject. Don't be "nice", be firm. Say right out: "Look, when you use my bobby pins and cover them in ear wax and then put it back with my other pins, your gross, disgusting ear wax gets all over the other pins and then into my hair, and this is GROSS, so STOP IT." Don't even say please. For serious, this is gross.
If you feel like you really can't do that, give her some of your pins in a cheap container like a breath mint box. Label it with her name and give it to her, and say pointedly: "Here, these are YOUR bobby pins. Do with them what you will, Ms. Ear Wax." Then make a point of always cleaning up your bobby pins and never touching hers.
Hope that helps!
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