Is this now useless?

This is not an activation, and she may not
perform actions during this time. On the
first game turn, she activates as normal.
On the first game turn, enemy models do
not need to Bull Rush in order to move
through her.

So I can't enter an enemy entrance and attack?

You really can't, since it happens before the first turn and there are no enemies on the board yet!

Get her into a position where they need to come by and go on overwatch, or make a fast dash to an objective on your opponent's side of the board. Or just plan on causing havoc by being in a position to attack early.

Infiltration is definitely not useless. Eva's free move happens prior to the first turn, so if you won the Set-Up roll and have to activate first, you can basically perform a back-to-back move with Eva. That could be especially handy when combined with overwatch.

Or, use Infiltration to bring her onto the board through your opponent's entry point, wait until he moves a character onto the board and then activate her to move/attack. She'll probably have to withstand at least one attack (that she could counterattack), but such a move is pretty suicidal anyway - done more for the shock and awe factor than any long-term gain.

Ah!

OK that makes sense. I can see some strategy for adding her to your side of the entry point.