I see where you come from, though I don't agree with your point that her bond with Lee should be stronger than with her parents just because she hasn't seen them for a bit over 3 months. Her parents were her reason to go on, they were her character motivation. Her seeing them was for her the hardest thing to encounter the entire season for her personally (though not for us as players because we didn't know the people of course). If there was a moment to break down completely in denial, it was then.
Heck, I imagined her doing that really "No Lee, they are just acting like Walkers just like us!" and get them both killed..
But she didn't, she conquered that moment and saved Lee after he fainted. She was long passed the denial response already as it was shown in that decision of hers. For her to then fall into denial a few minutes later when Lee shows he was bitten would have her break already defined character.
I understand your point entirely, though I appreciate it wasn't done by Telltale for those reasons.