D.B.
Is she a sound sleeper? If you're convinced that there is no infection, can you put the other earring in during the night when she can't flinch or fight you? If it goes in easily, great. If it doesn't, then stop. If that doesn't work, see if she'll agree to letting you numb the lobe with 2 small ice cubes (one in front, one in back). When it's numb (and you can tell by squeezing it a little) put the other earring in.
If the knob is big, then she could have scar tissue in there. You're positive it's not a reaction to the post itself, right? Some people have problems with nickel in the alloys. You could try switching to surgical stainless steel.
Otherwise try to get her to stop feeling she's a disappointment in any way. Let her know that some people's skin reacts to piercings. If you have to repierce, maybe have a doctor do it?
Good luck!