Subjective: The following part of this article is based upon the editor's personal experiences and opinions, and therefore may not be applicable for all readers.
This is one of the most difficult paralogues to defeat using "normal" strategies, especially on the higher difficulties. Almyra has read the strategy guide that Wyvern Lords and Bow Knights are very good, so if you hold back and defend, you'll have to deal with an onslaught of units with absolutely massive threat range, making it very difficult to safely position your units. As usual, fliers are very useful for maneuvering quickly around this gap and forest filled map if you choose to try to defeat everything, but be ready with the "Dismount" command if there's a Bow Knight in range of where the flier ends up. Which there probably will be.
If you're okay with missing out on the items to steal, a more sanity-preserving way to win is just to immediately try to complete the objective of defeating Nader rather than withstanding the onslaught. Nader is a physical defense tank, but his magic defense is very bad. The safest and easiest way is to move up to the center of the map using Stride on turn 1, then go for a turn 2 victory with a long-range magic user and another Stride use. Warlock Dorothea with 2 Meteors and a Dancer to let her Meteor twice on turn 2 is probably the safest way. Hanneman also packs Meteor if you've built him but not Dorothea. If you want to get up-close and personal, Linhardt's Warp spell on turn 2 can help a Stride'd mage also get in range of Nader (Lysithea as well, if you recruited her). If you're set on stealing the Aurora Shield, Warp can also be used on a thief to set up that steal before raining magical flaming rocks on Nader.