There is the stock radio which I assume is what she's running, an update with leaked OTA system 5.5.893 which updated both 3G and 4G radios, and updates 5.6.893 and 5.7.893 which each updated one of the radios, I think.
EDIT: Oh there's also a 5.8.894 update out there but I haven't seen anyone confirm if there's updated radios with it so I'm leaving that out intentionally.
You cannot just update the radios without applying the whole update because our bootloaders are locked.
And yes applying any of the updates will very likely take you off the "upgrade path" which means that whenever they get around to releasing the official update you'll have to wait until the dev community figures out a way for us leaked updaters to apply it.