Actually I had the problem in my first playthrough too. According to this site she should turn into a sage. But in these screenshots you can see that it doesn't work. I know from my first playthrough that Sara could be promoted, so why not Linoan? Does she need a special promotion item I haven't heared yet or is it one of FE5's bugs? Idk which translation patch I'm using. A friend of mine sent me the link (I can't find anymore) since the patch on SF didn't work for me.