Nereids Can you post some more pictures of the plant in question, and in natural light?
And sorry: I forgot it was your first grow. I took for granted that you knew more than you do right now; my bad. I've only been growing for almost three years and at first, I didn't understand that deficiency symptoms can so easily be the results of nutrient lockout because the nute companies like to tell us to use more nutes than we need to in order to sell more of their product.
So one strain may tolerate lots of nutes, where another strain is a delicate eater who doesn't need as much. I grow four different strains in each of my two hydro boxes, and I always make sure that none of them has special nute needs,--or that they all have more or less the same needs. Your plant may have stopped growing because of nutrient lockout, and she may recover and bounce right back.
Once the plant is in flower, we want things to go as smoothly as possible so that there is no negative impact on bud development. One grow I had a horrible case of root rot, and it stunted the growth of the buds, but the buds were still quite good. So your baby may be a runt, but she can still give you great buds.
Here's the breakdown on how to flush a sickly plant:
https://www.growweedeasy.com/flushing-sick-cannabis
I also recommend that you talk to her, tell her you're going to stand by her and nurse her back to health, and that you love her unconditionally. It's true that I'm an old hippie and all that cosmic shit, but I really believe that Cannabis responds to our emotions and disposition toward her. Which is why I worship my plants; I'm their servant, and they reward me with the best medicine!!! I just don't get the folks who get mad at their plants; they must have have had bad parents... ;-} We are here to help!!