I'm trying to figure out the questions being asked, but here is my attempt at answering.
As far as it goes, he had to use skill points in order to get his skills activated. So far, he has attack up and defense up, which took up his two skill points he already had.
Based on how it goes, it seems to have a time limit. So, while not limited to a single use, it may not last the entire fight either.
And as for why she wasn't in the party... it seems she was never part of any party in the first place when she went into the dungeon, so she may have met them while in there shortly before encountering the redface.
Edit: Yeah, you can see she wasn't part of their party from what the dude said in the bottom panel of page 6(note, including the cover and warning pages), they were escorting two rookies in the dungeon who seem to be the ones cowering on the ground. Manager-chan just went out of her way in order to help them survive the encounter.