What is her motivation (an affair or to leave her husband for you?)
All right. You are somewhat familiar with what she wants. The objective viewer's answer would be- this may be an opportunistic woman (if you are seeking long term relationship and commitment, she may not offer you that. She is already entertaining the idea of possibly cheating and using her husband (for whatever she needs him - $, flexibility, etc)
On the other hand, if you think that she's made a mistake and the two of you had found something in each other that you were lacking, then a relationship can fulfill those needs.
The question you would want to ask yourself is- what is it you want out of it and for how long. When people first fall in love, things are always "great" As they learn about each other and lose the energy to impress one another, they become stagnant like in a marriage.
I'd be up for a "casual" relationship but ideally would like to be with her for a long time; from what I've learned about her. I'm sure the last thing to do is approach her with this question but any other ideas how I can indirectly give her the idea that I'd give my kidney to be with her? Any signs I can look for to tell if she's interested? Not sure if she's entertaining the idea of doing anything other than being friends but our conversations feel a lot like the early part of a relationship. She introduced me to her husband last night, if she were into going to the next level would she introduce me to him? Not sure if she knew he was going to show up.
She could have introduced you to her husband either way. If she is interested in something more than friendship, you would know (she would be coming onto you)
It is also possible that she wants a friend (women can have male friends)
As far as letting her know how you feel, that would come on too strong after such a short time of knowing her. You may want to exercise some caution and not push her away. Try to interact in the same way (what made her interested in you as an individual) If she becomes interested on another level, she would be the one to let you know. She has to deal with her married status first (whatever that means to her)