Why would Thyroid Biopsy be inconclusive?

My wife noticed that area around her thyroid had slight bump. So she had ultrasound done but it was inconclusive. So she had thyroid biopsy done but that was also inconclusive. Doctor's office told her that not enough sample was taken to make a conclusive determination. So Doctor's office is recommending her to see a specialist. My wife is furious because her medical bills are piling up ($1300 for biopsy) and hasn't found anything out yet. Is this normal or did hospital lab screw up the test?