Yes they can still be banned, but they need to go into the gear icon tab and add the name manually, so you may need to keep track of the name for the model, so you can have her ban them, or send it in a PM for her.
In the chat window, where it has Chat, Users, PM, on the right side of that is the "gear icon" tab, this has extra settings in. Scroll to the bottom and there should be a blue text link that says something like "View/Edit ignore/banned list". She can manually enter anyone's name here, and set the ban to last only 30 days or be permanent.
If the user is being rude etc then of course silence them, but have a little discussion with the model first so you know what kind of comments she is ok with, and what the rules clearly are. For example, some models will allow a little bit of dirty talk in the chat from tippers, but not from greys, and if they do it they can be silenced. Basically, just talk, and even if you don't figure everything out instantly, it will happen eventually once you have seen certain messages, situations etc. Just don't get too trigger happy. If you are already a regular you probably have a good idea of what she already likes or hates from guys in public chat.
If there is a message or situation where you're not sure, give her a quick PM or tipnote to ask her, or see if she silences the user, then you can learn from that.