So why did she care either way if the loop continued?
She wasn't looping any more.
Presumably she could die and would just be dead (until Keiji died and rewound 30 hours (before they killed the server and the mimic backups)).
Or was it the case that she technically could still loop, but hadn't died since the end of her first battlefield and never triggered her time rewind? In that case, if she did die (before killing the server and backup mimics), would she wake up the day before her first battlefield? Or would she wake up 30 hours before Keiji's first battlefield? Would Keiji retain his memories (presumably not, since she didn't keep her memories when Keiji died and rewound time)?
She had literally no reason to care about the time loop anymore (apart from the headaches caused by the tachyon poisoning which, presumably, didn't go away (although she didn't seem to be affected anymore)).
Sucks she died, but only because it was unnecessary. I think this is why the movie version made it related to the blood, and she had explicitly lost the ability to loop - and that in the movie, her motivation for helping is to win the war - not to escape the loop... which is questionable in the manga since it's not clear if she's even still looping.