Need advice from women unable to conceive.

Okay so I’m currently pregnant and my sister in law has been trying to conceive for about two years now. It’s hard to talk to her about the pregnancy because I can tell how bad she wants it too. I want to help. I know it’s very possible that they can get pregnant. They have both been tested and both came back normal. But by some chance it just doesn’t happen for them, how do I bring up to her that I would be more than happy to be a surrogate for her? Like I feel like I would be helping. But I don’t want to throw the fact that I can have kids in her face, you know? Because that’s not what I would want to seem like I was doing Should I wait until she gives up to bring this up to her or would now while she’s trying be a good time. I’m just not sure how to approach the topic. I just want her to know how much I would love to help her if worse came to worse.