From a once over:

• I am not a native English speaker but //Element to print HTML confused me, I thought you meant that element would be printed. Maybe //Print button selectors  ?
• settings should be declared next to defaults, otherwise delete settings; is meaningless in destroy
• elems=$(settings.elems); should be var elems = $(settings.elems); otherwise you pollute the global namespace
• You declare var i twice in a for loop
• You should consider removing the iframe in destroy

All in all very clean, maintainable code.

From a once over:

• I am not a native English speaker but //Element to print HTML confused me. Maybe //HTML elements to be printed?
• delete settings; is meaningless in destroy ( see comment )
• elems=$(settings.elems); should be var elems = $(settings.elems); otherwise you pollute the global namespace
• You declare var i twice in a for loop
• You should consider removing the iframe in destroy

All in all very clean, maintainable code.