1. She must; everybody must - they will not let her in without it (We were there a month ago, wife's from Belarus, but plenty of Russians there as well). The only difference for non-Polish citizens is that the only choice is to get the passport picked up at Mailboxes.
2. Create the profile at the link and follow the steps. There will be an option for Mailboxes, it's in the center of Warsaw (more or less).
3. Yes, pick the "NVC scheduled appointment" option in the combo box, fill in the case #, passport, etc. You will get a QR code in the end with Name/date/passport details. Print, bring it. That's what they ask for at the door.