Need Advice About Talking About WLS With DIL

 I'll add my vote for staying out of it.  She knows. If she wants to talk to you about it, she'll come to you.

Wow, this post strikes almost too close to home!  As a women who's been in your daughter-in-law's shoes, I also add my vote that you not go there.  Like others have said, if she knows you've had the surgery and wanted to know more about it, I'm certain she'd ask.  I only know of one person that has had it and when I was ready I asked him.  I personally am scheduled for RNY on February 27th and have NOT told my in-laws because of my MIL's meddling and gossipping about everything to everyone. My struggle is the opposite of yours - how to bring it up to them!  I promise, I'm not saying this is you and I realize your heart is probably in the right place, but as much as it "hurts" you, I can guarantee it is killing her inside.  I beat myself up everyday tenfold for my infertility problems and I don't even know what they are.  I search relentlessly for answers and ask questions, have had tests, accupuncture, hypnotism for relaxation, meds, hormones, counseling, you name it.  I pray for some kind of meaning everyday, cry, cry and cry.  Having someone remind me so blatently would only crush me worse.  BTW, I have been tested and tested for things and appear "fine"?  I am MO with about 100 lbs to lose, but none of my Dr's have even stressed that oddly enough . .  it's a decision I've made for myself and I think she needs to make some of her own.  It's a painful journey and no one can truly share it with you.  I have fibromyalgia and acid reflux and am physically miserable, but otherwise I do not have PCOS, diabetes, etc. yet I've painfully miscarried three babies and gone through long periods of infertility in between over a 5 year period.  Much of this I know contributed to my weight, I wasn't even heavy part of the time . .  I was blessed, with the help of clomid, to finally have a beautiful now 2 year old son, but we're back in the very painful cycle again.  At almost 36 years old I feel even more stressed that I'm running out of time and I too constantly hear of others on FB, etc. having babies that shouldn't be . .  15 year olds and so on.  Someone said these things almost killed her.  Me too and it still does.  My MIL tried to tell me one time that she "understands" and that was the worst thing she could have said.  Besides our last name, being female and loving Jesus, there is nothing about our lives that we truly have in common, as kids or adults or mothers, and for her to say that was infuriating.  Anyway, I could go on and on . .  sorry, just close to home and got me emotional.  Yes, I definitely think you should take her to lunch or coffee and try to get to know her better.  Maybe you could go shopping or say you need to start walking and thought it would be an opportunity for you guys to start something you do together and spend time together.  You could non-chalantly bring your own surgery up in conversation at some point down the road.  I guess I'm saying, offer to be there, offer to love and support them unconditionally, offer to do anything you can to help, but do not "tell her what to do" about it unless she asks for your advice. 

I would never tell her, or anyone else what to do.  I have bent over backwards not to interfere in any of my children's relationships because I have been there, too, and the worse thing is family interference.
I do spend time with her but it's always with my son mainly because they really are inseparable.  They both work a lot and like to spend as much time as they can together.  They are the cutest couple I have ever seen, they are so close.
I really do understand about infertility.  It took me four years to have him.  I did adopt my first son but I went through a lot to get pregnant, including two surgeries and fertility drugs, including injecting myself.  I remember how my heart would break when I would hear about someone else getting pregnant or having a baby.  
I have decided not to say anything.  Too many people are saying it would be too painful and the last thing I want is to cause any more pain.  I do have faith that they will have a child.  I don't know why but I just don't doubt that, maybe because of what I went through.  And medicine has come a long way in the last 27 or so years so it will happen for them.