why is it that it seems ok for emma to lie but god forbid anyone lie to her, she just goes to town on them?

I think it's just a part of her character. Anger is a defense mechanism for Emma and after she has been alone for 28 years she's become fiercely independent. The thought of being lied to (I'm not sure in what situation you're talking about here) would be abhorrent to her, especially if they did it to protect her. Doing something to protect her oleh doing something wrong to her would bring up the great betrayal of her past and she'd wonder if she could trust the person who lied. Of course, then her walls come up and she tries to protect herself from further heartbreak oleh putting up her defenses: anger.

She did lie to Henry, but she is his mother and one of her strongest instincts would be to protect him. Thinking of Neal hurts her, and her need to protect herself from pain oleh thinking of Neal would have spilled over onto Henry. What if Neal hurt Henry the way he hurt her?