Yes, that is also acceptable.
As I pointed out once, the pattern Duo is using now V + 了 + Direct Obj. is better used as a clause rather than a stand alone sentence.
But it was not when I tried it (as of Jan 20th 2018).
Should also be correct, but it said I made a mistake
她已经买机票了 should also be accepted. Reported it the 11/02/2018