Your niece came crying to you that she had wasted 9 precious fertile years on a man who kept lying about having kids.How would you help her?

In one sense, this is sad, but your niece bears a lot of the responsibility for this.  I can see where a year or 2 might go by, but she CHOSE to stay with him that long, watching him lie and evade the issue.  I also think she made a mistake marrying him in the first place.  The one major issue where compromise isn't possible is this one.  She missed some red flags that she ended up marrying a guy who doesn't want kids.  Maybe she was leery of asking the very tough questions.

I'm not saying this to insult her, but if she doesn't identify her role in this, she's likely to repeat the mistakes.

I am so sorry for that,  but please let her know that help is available

just encourage her to adopt

I would just offer her comfort and say sorry things worked out that way. What more could you do??

Everything happens for a reason even if awful in the process. It’s unfortunate that she hasn’t had a child with her husband up until now hopefully it’s not to late for her by other means if applicable and it’s something she might consider. Is she still with her husband? If not has she considered adoption or other means even if it’s not with her husband? Just questions and statements not being insensitive just trying to give her some hope of possible. I pray if it’s meant to be she gets what she wants . 

Did he suddenly tell her he didn't want kids? Otherwise how has he been lying to her?

If it were my niece, I would simply support her in whatever decision she makes for herself, but not interfere otherwise.

I can't manage another adult's life for her.  Neither can you.  She has to cope with it and find a solution if she wants to come to a solution.

She is in the situation because of decisions she made. If it were me I'd stay out of it. 

There's not a thing you can do.  

I have no idea how old she is but I got married at 23, didn't have my first until 31, my fourth right before my 41st bday.    All healthy.

I guess she has to decide if her resentment against her husband (understandable because that is a terrible deception) is enough to divorce.  She doesn't need a husband or partner to have children in today's world but I've known people who have gone that route: even though they were financially secure its a rough road to single parent.

Baby fever is a real thing, no judgment but ultimately its selfish.  Its looking to future children to fill a hole within.  

Sounds to me like she has some work to do on herself.  So much of our suffering is caused by unmet expectations.  

Proverbs 15:22 says: “There is a frustrating of plans where there is no confidential talk.” The Hebrew word translated “confidential talk” implies intimacy and is rendered “intimate group” at Psalm 89:7. It would therefore involve, not mere surface dialogue, but honest and fervent communication in which both parties reveal their deepest feelings.—Proverbs 13:10.