Be your authentic self with her (and everyone)... And if that means that at some point, you are sad- than so-be-it. You shouldn't have the extra stress of 'putting on a forced smile' to her.... If you end up laughing around with her, that's great too. If you use your energy to keep up appearances, you will loose out on using your energy to just be yourself (that sounded better in my head, I hope you get my point?)
I keep thinking of a scene in Xmen: First class. The blue chick (forgot her name) was working on a weight bench (struggling to get the weight up)- she was in her 'normal' girl form. Magnito walks in and tells her that she's using too much energy/strength on focusing to keep up her appearance. At this point she relaxes and her 'blue' self is revealed.... When she tried the weight again, she does it with no problem.

When you use too much effort (mental or physical) to present a certain appearance, you will loose your real 'strength' that allows you to do your everyday tasks.

When I visited my MIL, I cried a little with her and we had some fun times too. She actually told me that she saw me as the person that her son fell in love with (the best validation I've received for my changes) This is your chance to show her who you really are now, and perhaps she'll pass on her observations to H.

M-31, H-31
T-9, M-7
S-6, s-20mth
sep 8/1/11
ILYNILWY 11/29/11
Creating separation papers.
Discover H has feelings for BFF, she does too 1/11/12
H moves out 1.20.12