UPDATE: SHE ADMITTED THERE WAS NEVER A BABY! my sister in law is lying about being pregnant!!

Her supposed due date was dec 15th with a baby girl (#3 for her) - they even picked out a name and told the whole family. Meanwhile I was diagnosed with infertility due to PCOS in August after TTC since January & experiencing very irregular periods & anovulation. I had my suspicions that she was lying in August when she and her family of 4 was living with us, she wasn't showing at all and was still smoking cigarettes (she even refused to lift anything when we were helping them move because of her "pregnancy" - while sitting there smoking). Again on thanksgiving she was at our house & tried to hide the fact that she didn't have an 8-1/2 month baby bump with a sweatshirt (as if that's even possible)! She has a history of lying & her parents even called her out on her imaginary baby last week. It infuriates me that she's still lying about this & she won't admit that it was all a lie. My hubby doesn't get why I'm so upset - but it's so wrong to lie in my family & it hurts me that she's so insensitive to what her brother & I are going through (we told everyone of our problems conceiving because they've always pressured us about babies & it was just getting unbearable for me). I need some serious advice on how to handle his situation with her & discuss it with her like an adult. Part of me just wants to be a bitch and call her out, but my hubby would be so mad at me, I'm not going to do that to him. 
UPDATE/EDIT: Thank you, everyone for your kind comments and support! I understand those of you who think she may just not show, but I was around her when she was preggers with her almost 4 year old, she was showing by 6 months & talked non stop about being pregnant. "Baby's foot is in my ribs, she's doing somersaults, etc" especially when the attention was not on her at the moment. We all knew what hospital she was going to have the baby at & we knew as soon as she went into labor (she even posted about that on Facebook). This time it's radio silence unless someone brings it up, then it's one word answers & she changes the subject. This is supposed to be her new hubby's first child, and even he is silent. My hubby is excited about us even having a chance at conceiving right now! When we do get pregnant I know he will be ecstatic! As a normal first time father to be should be! 
I'm going to do my best to absolutely ignore her, if she asks me what's wrong I'll be honest without being mean, & tell her how she's made this difficult for me. I wish I could count on it imploding on her, that's really what I wish would happen so maybe she'll realize how sick she is and get help. But knowing my hubby's family, it'll just blow over & no one will ever talk about it again. Hopefully I can get my own satisfaction by getting pregnant & being happy with her brother. The excitement his family will have when we have a baby will hopefully make her realize what a moron she is. The best way to "get revenge" (if that's what we would call it in this situation - it's the closest I can think of) is to be happy yourself right?!  Thanks again ladies! I'll keep you all posted if anything happens! 
FINAL UPDATE: SHE FREAKING ADMITTED THERE WAS NEVER A BABY! My husband asked her what's going on with the baby when we saw her on Christmas and asked if she was ever even pregnant. She said no! I asked why she lied for so long and if she understood why she hurt me by doing so. She nodded that she did. Unfortunately our conversation had to be cut short because this was literally through car windows as she was heading to work and we were leaving. I appreciate my husband doing such an awkward thing for me, I know that's never easy, especially at the point his family is in with her. She claims her husband knows and that they're TTC now, but we aren't so convinced. They have baby gates up in their house "for when the baby comes." Whatever, I don't care if she's lying to him still, she had to come clean with us and I was able to let her know that her actions affected me and our relationship as sisters. I did tell her that we can talk further at any point, and that I'm here for her.