you keep saying you dont want to hurt her transplanting, but you hurt her worse by not. her dirt is too much for her to get her roots into. it needs some of those white bits (perlite) in it - the white bits loosen up the soil and the roots like it. you cant just put it in and mix it, you have to add it to soil before planting, then mix it really good, then pot the plant in it.
when you use a 20L pot, you need to fill it up. you need all that room for roots. a half full pot is not good, a 5 gallon pot is shaped and sized to hold 5 gallons, not 2.5 gallons. if you get a 2 gallon pot you will notice it is taller and skinnier, that is on purpose. get a smaller pot if you want a smaller pot, but do not half fill a bigger pot.
everyone has advised you to transplant. you need to decide and either do it or not, but the longer she stays like that the less chance you have of getting to smoke her.
you cant take a shortcut and just dump perlite in it. you NEED to transplant or toss her and start over.
you cant feed her out of a bad bit of dirt and the wrong pot. no matter how you adjust the feeding, she cant get the food if her roots are mad at you.
you wouldnt like it if your mom kept you in a toddler bed because she was afraid a bigger bed would hurt you... if you want to grow up and see your potential, a bed the right size helps! your girl needs a place to stay with more room and better conditions or growing up wont happen well