Mask yourself stoic, uncaring.  Your mother will sit awkwardly, you'll let her, you'll leave.  You'll ask yourself why did she even come in the first place, there are two choices when you have kids you stay, or you stay the hell away.  She'll leave and you'll go back to life as usual, not hiding your loss, not letting on that it's a loss at all.  She'll friend you on Facebook, and you'll grimace every time you see "Kelli B likes your photo" because it isn't fair that she gets to look in on your life after leaving you to build it all on your own.  You'll grimace and pretend to let it go, masking it casual, normal to have a drop-in mom with half a set of teeth.