Credit to PsychoSlammer.

1. Open Creation Kit

2. Select AVLA mod as active and Dawnguard as master, "yes to all" warning.

3. In the Object Window box filter for "outfit", right click any outfit, select duplicate. Open duplicate outfit and change name to (example: SeranaOutfit) select armors and click delete. 

4. Leave open, go back to Object Window and filter for AVLA, select the AVLA_ArmorLeatherBoots01, AVLA_ArmorLeatherCuiras01 (01 is brown) and AVLA_ArmorLeatherGauntlets01 and drag them into the Outfit box then click ok. Select NO to create new file then select yes to "are you sure".

5. Go back to Object Window and filter for Serana and select DLC1Serana, click "inventory" tab then the drop down menu of "Default Outfit" and select the outfit you created then click ok and yes to any warnings.

6. Go back to Object Window and find the two files "DLC1SeranaOutfit" and "DLC1SeranaOutfitHooded", right click both and delete. save and move the newly modded AVLA in modmanager above Bijin or Seranaholic mods. 

if one is using Seranaholic or Bijin mods then the VampireLeatherArmor.esp needs to be higher up in load order to keep the dark face from happening.
open VampireLeatherArmor up in SSEEdit along with Serana.esp then right click on VLA and select "add master" then tick Serana.esp and close.