Seriously, Wendigos appear all over the place. Near Galbadia, Wilburn Hill, Obel Lake, Hasberry Plains - It's a very common enemy.

As for Angel Wing the mechanics are complicated, but the jist of it is that Rinoa goes into an uncurable Berserk mode and will constantly cast any stocked spells she has. These spells aren't used up.

If you care for more detail: She is immune to Confuse and Silence also, and will automatically become "unsilenced" on using Angel Wing. Only Death or Petrify can stop Angel Wing. If she's Stopped or Sleeped then she'll carry on after being cured. She will never cast Cure, Cura, Curaga, Life, Full-Life, Regen, Esuna, Haste, Double, Triple, Protect, Shell, Reflect Float and Aura. She will use any other spells currently stocked. She never targets your allies, only the enemy. If the spell is single target the target is chosen at random. There's no real pattern to what spells she casts, though in general she'll prefer status/low level spells to higher ones (e.g. Ultima). So for maximum effectiveness have all of the non-casted spells, then put in maybe a mix of Meteor/Ultima. Since these spells won't be used up you can easily junction them also.

Hope that helps.