For female Phicens there’s a variety of heights and physiques.
I found a great page at Giantoy that details the differences.
I’m leaning towards S27B which would have her height at just shy of 5’ 1” (five feet and seven tenths of an inch). Bust size for that figure is medium. Tanned body.
My thinking on this is that making her relatively tiny accentuates the sense that she is your kid sister and sidekick. Similar to the idea of halflings’ natural gift for thieving, the fact the she’s small could be an asset to stealth.
As I’ve mentioned, I keep her as pure Thief and equip her with the Shadow Armor and Dagger of Venom. I send her in to backstab enemy spellcasters to disrupt their spellcasting with the DoM’s venom drip. Then she scoots away to use her shortbow. And/or to fire her wand of Magic Missiles to continue to disrupt enemy spellcaster’s spells.
But anyway, I think the smallest size is probably a good way to go. If you’d like to weigh in, you can do so here but I’ve also posted about it on Reddit’s r/Baldur’s Gate sub: https://reddit.com/r/baldursgate/s/YLQOnEFFj0
Update:
Well, despite a Google search saying 5’ 0” it doesn’t appear to be officially sourced.
In thinking on it more, the 5’ 1” stature I was envisioning seems a bit too small. Plus as some have pointed out she is a Bhaalspawn.
Looks like about 5’ 4” is the consensus. And I would agree this feels right. It’s also a little more consistent with her being a badass backstabbing thief, at least as I play her.
According to Giantoy’s chart (https://giantoy.com/blogs/guides/tbleague-phicen-standard-female-figures-comparison-with-photo-body-shape) Phicen S29B with a head on it is 27.2 cm, which by my calculations corresponds to 5’ 4.25”. So That’s probably what I’m going to use. https://giantoy.com/cdn/shop/products/847a76c98fe02c24ec2f87f32759ba3c_701x688.jpg?v=1603372752
One Sixth Baldur's Gate 
