How large should the root-ball be?

Here is my problem-plant. After trying everything to help her, someone suggested to transplant her into another pot with better soil. Below are pictures taken a few hours after her transplant (pictures of the bottom half, the middle and the top of the plant). She hasn't went into shock yet (she looks the same or maybe even a little better since the transplant). But when I transplanted her, her rootball was as big as my fist. For a girl, I have a good size fist, but I would think that her root ball should have been bigger than that. She is 7 months old and has never been pruned or topped. She is 20" high. We recently made an indoor grow room about two months ago and had moved her from being outside to the new grow room where she has been the last 2 months. She was lookin pretty good till we kicked her into flowering then she declined again rapidly. So i'm thinking it has somthing to do with her roots being small (unless she's suppose to have small roots)

Poor soil can make the roots not grow right.
Her roots, were she healthy, would fill a gallon pot.
Glad she's in a better home now!

for a 7 month old plant the root ball should have been alot bigger. What size pot where you in and what size are you in now? Water with Superthrive to easy transplant shock. Remember the rule of thumb is 1 gallon per foot of verticle growth.

The pot size didn't change. 12 1/4 inch pot, maybe 3 or 4 gallons? I put her in a pot that was a replica of her first. ( I don't want my husband to know I transplanted her) If he knew I went against his wishes he'd be pissed, but she looks so much better now. Her leaves are not curling anymore and she's not abit droopy. Hopefully she'll stop yellowing. She's 75% yellow.

Sounds like you have the right pot size, what was the planting medium before and what is it now. Try foliar feeding with Fish emulsion to correct the yellowing quickly. The droopiness may be caused by over-watering.

The medium it is now ii is E.B Stone Organics - Edna's Best Potting Soil. Enhanced with a special blend of bat guano, worm castings, kelp meal and a bunch of other stuff. It's supposed to be one of the best. I added more perlite because I didn't see a whole lot in it. Before it was just a cheap potting soil from walmart (no added plant food or fertilizers like you get with miracle potting soil) Then I added sand and perlite to it. It seemed alright at the time but now I know better.

As far a the fish emulsion goes, how much per gallon? Do I go by the back of the bottle or is it different for cannabis (seems like everything is)

Oh and Smoky,
How often am I supposed to spray her (once a night, once a week, once a month?)

On the bottle of the fish emulsion it says for indoors and house plants use 2 tsp per gallon. Then It says Avoid wetting foliage. How am I supposed to foliar feed without wetting the foilage?

don't go by the back of the bottle, use 1 tablespoon per gallon, for your plant. Spray her once a day until the yellowing improves. Trust me, I do it all the time but beware it stinks to high Heaven! Sounds like a great planting medium to me and that you found the 'root' (no pun indeeded) of your problem!