Which line in this excerpt from chaucer's the canterbury tales contradicts the claim made in the third line that the prioress speaks fluent french?

her greatest oath was but by saint eloy!
and she was known as madam eglantine…
and fair she spoke her french, and fluently,
after the school of stratford-at-the-bow,
for french of paris was not hers to know.
at table she had been well taught withal,
and never from her lips let morsels fall,…