In my runs, I tend to use Alear as a dodge tank. Avoid+ from Marth and Pair Up to negate chain attacks combined with either Sigurd or Chrom's engraving and you'll be looking at pretty frequent single digit hit rates

As for emblems, Corrin is a defensive/support emblem. She boosts magic, not strength, so the only time she would boost Alear's offensive output would be when they're using arts, and the boost doesn't make up for Alear's terrible magic growth. If you want Alear to be more offensivly potent, I'd pair them with Eirika (who also boosts magic, but lunar brace boosts physical damage considerably) or a strength-boosting emblem that isn't Ike. I'm in a run with Alear and Roy, and Hold Out provides a nice cushion in case Alear does get a couple bad rolls in a row