Yes, this must be her decision, not yours. Sure, a particular judge may enforce a protocol barring a new spouse from playing a role in the proceedings. But it's also possible that your presence could have an emotional impact on either or both parties. Your wife might be flustered by having to put herself back into an earlier time in her life, while at the same instant having you there to pull her into this time. And the ex might simply be angered by the evidence that she's made a happy new life without him, instead of being the weepy loser he imagines her to be now.
Do what her lawyer says. If he has no opinion, do what she says. If she expresses no opinion, she might just be stifling the urge to tell you to stay home. If she wants you there, odds are that she won't have any reservations about saying so.
Perhaps you should make it clear by saying something like, "If you want me to be there with you, I'll be glad to. But it's your choice and I'll understand if you feel more comfortable without me." That gives her the option, and the relief of knowing that either way is okay with you.
And please remember that the crap won't be over when she gets home from the hearing, regardless of which way the ruling goes. She'll need your patience, kindness and support for a long time. You're going to have to make sure that none of what happens next is about you.