A nun does not cover her face on the bus, or anywhere.  Not a good comparison at all.  Also, a nuns dress come from a much different place than a Muslim covering.  A Muslim woman covers so as not to tempt other men.  A nuns habit is worn out of modesty before God.  Completely different.   In the early church, in Christ's time and after his death,women were to be veiled in public, because they were seen as possessions. 

No where does it say in the current catholic church that all women should be covered head to toe, except it was a tradition (rule?) in the past that women cover their heads during Mass.  The old tradition of keeping women covered during Christ/the apostles has been dropped, for good reason:  women are NOT possessions of their husbands.