"Oh!" Sinead started as Professor Newton appeared behind her, apparently out of nowhere, and temporarily distracted her from the portrait. "Er- good afternoon, Professor. I'm... not sure?" That was true enough; she was pretty sure the house elves didn't normally clean these portraits, but if they didn't, why was one just sitting here?

The portrait himself didn't seem entirely clear on the answer to that, either. She glanced at Augustus (as he was pronounced by a small plaque on the frame), unclear whether or not he was somebody who needed to command her respect.
"I wasn't sent here to clean or anything," she clarified. This was the weirdest. After a moment, she started, realising she still held her wand- that was something she could sort out, at least, with a muttered "Scourgify" at her hand to siphon away the cobwebs.

This taken care of, she felt slightly more in control of the situation and looked over at Augustus once more. "I could clean the cobwebs away from your portrait as well, if you'd like," she offered. That would probably be fair recompense for mashing her hand into his face. "Why are you so dirty, though? Isn't there a man who cleans here normally?" She'd seen him making his way through the castle many times, and remembered encountering him just along this stretch of wall on the way out of her first History of Magic lesson.