Even tho Elena was in the middle of a party, she had never stopped her observation magic. So when the suspicious group started to gather outside she noticed them instantly. But without reading their minds she wasn't sure about who their target was. There were other influential people in the other rooms too.
But after detecting the adventurer-like dressed group and the masked figure she became sure that their target was definitely this party which Elena was a part of. It was a simple deduction as no group other than Elena's would need such strength.
So she cast a spell {Full Cure}. The objective of that spell was to completely get rid of the intoxication. After that she told them that some trouble was coming their way and that they should be ready.
Elena didn't just take care of all the trouble by herself as it was not needed. Letting them face off against this sort of trouble would be good in the long run. So she just gave them a warning.
