... leaked on Twitter that the network had asked the writers for extra episodes that would wrap up the series, so once these episodes were filmed it would be over.

The network denied this completely, saying no decision about Pan Am was was made, but all the signs suggests Vanasse told the truth (she would know if the production needed her to clear her schedule to film unplanned extra episodes, she was just not supposed to talk about it, and didn't realize that even her comments in French for her Québec fans/friends were scrutinized by the US entertainment media).

The actress in question (Karine Vanasse, another Québécoise like Jessica Paré on Mad Men) is already signed for another recurrent role in another US series if its pilot gets picked up, so it's another sign Pan Am won't be back (though she knows better now and simply declined to comment when asked!).

It was kind of a gamble that the main attraction to Mad Men was with the times it's set in, and its depth/style/writing/mood that confined it to a small audience on cable and huge critical success, and something more superficial & glamorous about the sixties would turn out to be as popular as Mad Men but with a mass audience. Apparently their guess work on what made Mad Men's success was wrong.