Since waaaaaaaaay back in Baldur’s Gate 1 & 2, Jaheira is canonically a Fighter/Druid. When you meet her in Baldur’s Gate 3, she is explicitly said to be an Archdruid – though she also has a Soldier background and likes to duel-wield scimitars.
However, we have to remember that FLAVOUR is not MECHANICS. In-universe, Jaheira is someone that likes to get in your face with both weapons and nature magic. How can we make that happen?
Just because you are a disciple of nature, it doesn’t mean you have to be a Druid. As a Cleric you can’t choose Sylvanus, but Mielikki and Corellon are both available.
More importantly, the Nature domain is available. This grants you proficency in Animal Handling, Nature, or Survival as well as a slew of spells normally exclusively available to Druids. Nature Clerics also get access to Heavy Armor, which honestly doesn’t feel that thematic – and you might still be happy to use Medium Armor for your actual chestpiece – but it gives you more options for helms, boots, and gloves.
Cleric of Nature is basically a Druid minus the shape-shifting.
Pure Cleric 12 is perfectly great and gains you three feats/ASIs.
One of your feats could be Dual Wielder. Main-handing a quarterstaff (such as Staff of the Ram) and off-handing Sylvan Scimitar (and later, Belm) would let you use your Wisdom for your attack modifier, minimizing how many attributes you need to worry about. Alternatively you could dual-wield two light weapons (Sylvan Scimitar and Belm) and skip the Dual Wielder feat.
Of course, you can always eschew the Wisdom-synergy and use any weapons weapons with the support of Elixirs of Giant Strength.
You could also do Sorcerer 1 / Cleric 11 to get proficiency in Constitution saves as well as access to Shield (and maybe Magic Missile?) – and Storm Sorcerer would increase your mobility. This would make you a stronger caster but dampen your melee combat ability due to feat starvation. I’d probably drop duel-wielding and pickup a shield instead since you’re a Half-Elf and always have proficiency.
But I think we could do better, theme-wise.
If you want to lean more into melee combat. consider Ranger 5 / Cleric 7. Note that Two-Weapon Fighting fighting style does NOT allow you to use non-light weapons, so you’ll still need the Dual Wielder feat. In fact, with Belm you won’t even be making off-hand attacks so you’re probably better off using the Defence fighting style instead. Ranger 5 does give you an extra melee attack per round. You’d still have access to level 5 (but not 6) spells. Unfortunately, you won’t get your Divine Strike feature from Cleric 8 – but the extra attack should more than make up for it.
If you want to be dedicated to her canonical dual-class setup, you’ll probably be looking for 5 levels of Battlemaster Fighter to get Extra Attack, with the rest being dumped into Circle of the Land Druid. This would limit you to 4th level spells, but you’d get two attacks per round (or three if you wield Belm) plus Action Surge. To keep your attributes sane, you’ll either want a +2 Staff (most likely Staff of the Ram) powered by Shillelagh to use your Wisdom (Sylvan Scimitar won’t cut it) or chug Elixirs of Giant Strength.
You can provide your own Haste by picking Arctic or Grasslands as your level 5 druid land, which fits with Jaheira’s evident self-reliance.
Alternatively, you could do Fighter 6 / Druid 6. You’d lose access to 4th level spells, but gain a bonus feat.
This works for Fighter / Druid (which can Self-Haste) or Ranger / Cleric (which has Command). You can also go pure Cleric (or Sorc 1 / Cleric 11) but you’ll lose the Extra Attack so you’ll be focusing more on control magic rather than melee damage.
Attributes: Con 16, Wis 17, and probably Dex 14 (even if wearing heavy armour). You will end up with 20 Wis with your amulet and one ASI boost. 22 with Mirror of Loss.
Start with five levels of your martial class first, if applicable. Fighter will get Constitution saves, Battlemaster Maneuvers, and Action Surge. Rangers will get better spellcasting and a Dire Raven companion. Either way, your fighting style should be Defence and NOT Two-Weapon Fighting.
Your feats will be a +2 Wis ASI and the Dual Wielder feat (unless you want to use a shield, in which case you can consider Alert, War Caster, or +2 CON). If you went pure Cleric, then you also have the option to start with Con 15 and pickup the Resilient: Constitution as your third feat.
As a Druid, for your Circle of the Land I’d suggest Coast/Underdark at Druid 3 (for Misty Step), Arctic/Grassland at 5 (for Haste), and Coast at 7 (for both Freedom of Movement and Confusion).
For gear, we’re going to want one piece with Crit immunity and one piece with advantage to constitution/concentration saves (or an Elixir of Peerless Focus.)
You could pursue the Helmet of Arcane Acuity and attack with Belm and then cast spells. Alternatively, with Band of the Mystic Scoundrel you can attack twice and then cast Hold Person (unless self-Hasted!) or Command (if Cleric) as a bonus action. Clearly this item combo would feel better with the Cleric variant than the Druid variant. Note that this might be contested by something like a Swords Bard (1F/1W/10B or 2P/10B), which would make better use of the items.
Helm:
Chest:
Gloves:
Boots:
Amulet:
Back:
Rings:
Main-Hand:
Off-Hand:
Elixir Options: Peerless Focus unless handled by gear. Vigilance for initiative, since you lack Dexterity or the Alert fleet. Battlemage’s Power to improve control spells.
Pre-Fight: Shillelagh and Haste, if you have it
NOTE on Arcane Synergy & Conditions: As of Patch 5, the game appears to only grant the bonus when afflicting an enemy with a condition, other than threatened.
Notes for Paladin variant:
I’m now convinced that rather than using Staff of the Ram + Shillelagh, you’re probably much better off using Flame Blade. Sure it costs a spell slot, but it’s a Bonus Action to cast and since it’s a Light weapon you don’t need the Dual Wielder feat. Belm offhand is still excellent, since it should swing your Flame Blade with its bonus action. I’ve left this guide as-is for people who still want to do Staff things.
If you want to be a Druid but you already have someone like a Sorcerer to Haste you, consider Circle of Spores instead of Circle of Land so that you can convert your otherwise unused Wildshape charges into Temp HP and bonus Necrotic damage. This also means you don’t need to stress about Concentration saves, which simplifies gear (and makes Risky Ring more appealing.)