Bud rot or something else?

The soil may have been high in K to start. Blended pre-made soils are only as good as the guy mixing in the parts of it! I've had store bought soil problems from faulty manufacturing before. Why I went to building my own and only trusting a cpl of pre-made for seedlings/special projects,

But it's NO DOUBT high K or K tox....

it was outside and it came inside ?

probably a bit too much K and the light shift from coming inside probably cause some shock and extra colouring

Looks almost black I like the colour hope you can get her to finish well

I believe the color is just from the strain itself. Fed it on two separate occasions & been keeping her watered. Seems to be thriving now