Dark red or purple stems is bad during veg. Not sure how effects flower. I can see your stems are tri-toned. Add bit of cal-mag to your watering. Or put your pH around 6.7 until problem goes away.
Hi, thank you guys! She already has a cal deficiency, which I know can cause a purple stem... but if that’s all it is then it’s under control - so I’m relieved - and maybe some of it is genetics.
If the plant is otherwise healthy (looks like it is) and there are no other signs of deficiencies, then it’s just genetics. Nothing to worry about. Good luck!