found young kitten

Found a small kitten inside the plant I work at, it’s been years since I’ve had one this small. I’m not sure how old she is, her eyes are open, can walk but very unsteady. Teeth are just breaking through.
I wiped her down with a damp cloth and dried her off. She’s eaten about half an ounce of kitten milk so far. She seems healthy; purrs, attempts to clean herself, was batting at my fingers.
I also own two adults females who aren’t happy with the new meowing baby but they don’t bother her, just slink around and hiss as they go through the room.
Any tips on care or an estimate of her age would be welcome.