Susan's anger at Ophelia had diminished somewhat after she'd had a bit of revenge on the other woman, but she was still angry, and she knew Seamus enough to know that he needed to work his aggression out in a (hopefully) healthy way. As such, when she walked into Finnigan's she simply followed Seamus up to the roost and ignored his brusque comments.
Once the wards were in place she shrugged off her coat and stood to face him in a battle stance. She waited for Seamus to commence, then smiled almost wolfishly. Instead of responding verbally, she sent a stunning spell hurtling towards him. It was fairly weak in comparison to what she normally would have opened with - Susan figured that there was no point in injuring her friend if she had to - but it would still hopefully pack a punch. She stepped back and snapped one of the stronger protego spells she'd learnt in her training around her to fend off whatever Seamus sent back at her.