Coming in from such_heights: I think the biggest issue with Lyra is whether or not you manage to convince her that the Ring is really evil and really must be destroyed.
Because if she really and truly believed that, the Ring wouldn't have a chance. This is LYRA. She is made of STUBBORN and LIES. If she decided the Ring wasn't going to get her, the Ring would fail to get her JUST BECAUSE SHE DECIDED - no virtue of her own, just NO I WILL NOT BE TAKEN OVER BY YOU I AM LYRA SILVERTONGUE AND YOU ARE JUST A STUPID LUMP OF GOLD.
On the other hand, if you haven't actually got her to throw herself into the fight with her entire being, the world is doomed.
Assuming a grownup Lyra.
Because if she really and truly believed that, the Ring wouldn't have a chance. This is LYRA. She is made of STUBBORN and LIES. If she decided the Ring wasn't going to get her, the Ring would fail to get her JUST BECAUSE SHE DECIDED - no virtue of her own, just NO I WILL NOT BE TAKEN OVER BY YOU I AM LYRA SILVERTONGUE AND YOU ARE JUST A STUPID LUMP OF GOLD.
On the other hand, if you haven't actually got her to throw herself into the fight with her entire being, the world is doomed.