Would a Predator even try to hunt her? Probably not if she is holding Newt and aliens are running around.
Ripley ain't dumb, wouldn't take long to realize that she can just throw her gun away and the Predator will ignore her.
If she's in the hive, she'd probably stay armed. She'd be risking running into xenos around any corner, without a weapon. Odds are she wouldn't fully understand what was happening before it was too late. Let alone make a correlation between being unarmed and being ignored by this new and unknown danger.
But, like you said, the presence of the child would probably stay the predators hand, and he'd let them go as long as Ripley didn't cause him trouble.
Nevertheless, in an area overrun with xenos, disarming herself simply wouldn't be an option. She'd survive the predator momentarily, only to be killed by the aliens.