Apparently, Wesley was no longer leading the defense and now Illyria was. Katara wasn't a very big fan of Illyria whatsoever, but she respected Angel's decision and she cared for Fred, the woman whose body Illyria was using. So she followed without question, a look of determination already hardened her normally soft and caring expression.
Once outside, she approached the former God and asked directly and simply, "Where do you want me to be?" With all of the water around, Katara knew she could serve in just about any area, whether it be the front of the defensive line or the very last. She didn't have a preference, either, but even if she did, Illyria was in charge. So she waited for a response and hoped the other woman could put aside their differences long enough to see the job through.