Strong vote for shingles. Typically the shingles virus (Herpes Zoster) follows a nerve and hers is in the exact path of one of the intercostal (rib) nerves. It developed with the time frame of shingles too. Yes, very painful and sensitive.
Not any real good treatment for it and takes up to three weeks - sometimes longer. The fact it has not spread very much locally and this points to shingles.