In Tuck Everlasting, Winnie has a conflict within herself when she returns home. What is it?

I think by "returns home" you are referring to after the constable brings Winnie back from the Tuck household.  

Winnie's conflict is what to do about Mae Tuck.  To protect Winnie from the man in the yellow suit, Mae Tuck attacked the stranger.  She clubbed him over the head with the stock of the shotgun. 

With a dull cracking sound, the stock of the shotgun smashed into the back of his skull. He dropped like a tree, his face surprised, his eyes wide open. And at that very moment, riding through the pine trees just in time to see it all, came the Treegap constable.

Unfortunately, the constable witnessed the entire thing, but didn't see that the man in the yellow suit was blackmailing the Tuck family.  The constable is forced to arrest Mae and take her to jail.  The other problem is that the man in the yellow suit dies.  The constable now believes that he has witnessed a murder, which means Mae is likely to be hanged. 

Winnie's is conflicted with what to do.  She wants desperately to help the Tuck family rescue Mae.  She wants to do something important, but she also knows that any actions that she takes will be definitely against the law and will get her into trouble.  

Jesse squinted at her, and then he said, "Yep—you know, it might work. It might just make the difference. But I don't know as Pa's going to want you taking any risk. I mean, what'll they say to you after, when they find out?"

"I don't know," said Winnie, "but it doesn't matter. Tell your father I want to help. I have to help. If it wasn't for me, there wouldn't have been any trouble in the first place. Tell him I have to."

Despite the risk to herself, Winnie decides to help the Tuck family break out of jail.