Two things are immediately evident to Juliana Blumenthal:

#1—her son and this woman he insists upon introducing are infatuated with each other (in fact they positively reek of consummation);

#2—Joanna, trim and fit as a gymnast though she appears, is pregnant irreversibly (filled out just enough to preclude a problem-free abortion).

Less apparent but on-the-spot intuited:

Sam is not the father.

            ‘Come in, come in. You didn’t expect to blurt out such stunning news then pull a sprint, I hope? Give your mom and future mom-in-law a chance to catch her breath; I’m in shock.’

alternately flattered by:

Sam’s eagerness to share what she presumes are the couple's heat-of-the-moment plans,

and aghast at:

how spontaneous, rash, and reckless the pair’s intentions are,

Juliana hastens to the living room’s makeshift bar for a fortifying drink.

            ‘I haven’t any champagne but here’s an excellent cabernet I’ve been saving for some special occasion...’

(... and what could be more special than a son proposing marriage to a three-month-pregnant stranger? is the subtext Juliana throttles, poignantly aware that there is more to be imparted by the agitated couple seating themselves on the sofa and opening a laptop module, fidgeting with controls to access a file in which is compiled she- knows-not-what but which makes Juliana nervous anyway, a premonition dawning that the revelations made thus far are relatively tame, that wilder more extreme assaults on her single-motherhood are itching to be waged, her heart already pounding, already racing in advance of some imminent disclosure).