Yes - she's going to have to sit aside for the first bit of the inevitable 'action'

Your mother looks exasperated at Fiona's abrupt reveal, obviously more than a little fed up with your sister. After a brief glare in Fiona's direction, she turns to Allison, who still looks somewhat stunned.

"Well, this isn't how I'd have brought up the topic, but I suppose there's no point in beating around the bush...the women in our family all have something 'extra'. We keep it a secret usually, but you're Jesse's girlfriend, and he seemed to think you wouldn't...mind."

Still looking a bit overwhelmed, Allison instinctively looks down towards your mother's lower body, though the table is in the way. After a few moments, she manages to squeak out a timid, "I-I don't mind."

Your mother continues speaking, and you notice a bit of relief on both her and Elsie's faces. Fiona just looks impatient, standing there with her cock out...

"And since it's hard to find people we're willing to trust, we end up dealing with each others' sexual urges...if you're willing, we'd more than welcome another participant."

You can tell that, for all the surprise she's still dealing with, Allison is more than a little turned on by the offer. To your gratification though, she turns her head to look at you, as if trying to see if you're on-board with the idea. You waste no time in nodding quickly, and Allison turns back to your mother. "I-I'd be happy to join in."

Your mother coughs delicately. "Well...no time like the present. To be honest, the room has started smelling like sex for a few minutes now, so I'm a bit in need of some relief myself." Elsie pipes in with an assenting, "me too" a moment later.

Fiona steps forwards as if to go in for the action, but your mother fixes her with a glare. "Not you. You haven't been behaving at all recently, so you'll have to sit out for a while...if you behave, I you can join in after a while." You hear her mutter something about how withholding sex seems to be the only punishment that has any effect on Fiona...

Apparently not eager to have cum flying all over in the living room or kitchen, your mother corrals the three of you towards her bedroom, with Fiona sullenly following behind.