It would be more work but maybe a non-OBSE and an OBSE Vilja version would be a way to go. Or if it is possible to just have an OBSE-addon but I do not know if that is possible. As for suggestions for next version:
1. Have her automatically repair her armor if going to sleep.
2. Have her repair her armor when asked through dialog.
3. Use appropriate weapon if facing creatures only affected by silver or magic. If she does not have such she should stay back and hide or just heal the player if that option is chosen.
4. Have her skills improved if using enchanted clothing or armor/weapons.
5. Be able to use better alchemy equipment.
6. Have an option on first dialog page to give her strawberries, sweetcakes, sweetrolls so I do not have to go through multiple menu options to get that.
7. If possible, some way to better interact with NPCs added by other mods. I only have once case right now where I had a problem. I have Frans and The Alyeid Steps installed, no other overhaul. I have the Frans Adventurers plugin which adds adventurers to the game which you can meet in dungeons. Vilja and I went into the cabe to activate the stepstone network and met two adventurers from Frans. I ws not looking at Vilja at the time but soon heard combat and she was fighting with them. We did have our weapons drawn when we ran into them. I interceded into the combat by talking to Vilja and was able to get her to stop. A few seconds later the adventurers attacked her again. Interjected again and moved away. One adventurer again came after her. Had to kill him with the console so we could continue. Further in the dungeon in an interior we ran into another adventurer and he got along fine with Vilja even when we had to fight a Minotaur Lord. I do not know how to find why the combat happened, and as the adventurers attacked Vilja after we got out of combat with them, I suspect Frans but do not know why Vilja was attacked. I am redoing my game again tonight to get a different configuration, also using Frans, so will keep an eye to see if it happens again.
8. Have Vilja recharge her weapons if she has full soulgems, if the weapon has 0 charge or if a soulgem would recharge it without wasting charge, unles it is at 0 then she would use the lowest charged soulgem she has to bring it to full charge regardless of waste.
9. Ability to recognize ingredients from COBL.
10. Ability to make complex potions is she has ingredients in inventory (like poisons, restore attributes), potions I would ask her for. This way I would not need alchemy in my skills and just have her the alchemist in our party.
11. Have Vilja recognize enchanted clothing as armor (my cheat to keep from having to repair her armor) so when told to relax she would switch those clothes to her dress. This would include hoods and cloaks which IIRC she keeps equipped even if relaxing.
12. Enter combat if player is in combat even against NPCs she does not recognize as hostile, as in the Unfriendly Competition quest fight in the tomb.
13. Not get mad at all if I hit her by mistake

14. Be a better archer (although the free arrows laying around are a nice bonus).
15. Stop combat even if in combat. Example when she detects enemies through a wall. I am not 100% sure, this is just a thought now. I can get her to talk to me in this situation and she asks if I want some help. If I say nevermind sometimes she stops sometimes not, or she will resume the fight soon after. Also, when traveling, she will attack a mudcrab which may have targeted me even though I am running past them. These insignificant creatures I ignoe at times at high levels. Not worth having to repair my weapon after a slice or two. This would go hand in hand if I want to run away from combat she should run away too.
16. When sneaking and we come upon two enemies it would be REALLY COOL to have her target one with her bow while I target another and shoot at the same time. or even target one so both our shots can kill the target. How cool would that be?
17. Put items in her inventory that instead of shopping she can go and sell for you.
Well, that is all for now

Probably only a few are possible but I would never know if I didn't ask.