It could be it could also be a macro nutrient problem could be a lack of iron. It could be a toxcity but usually that would start at the tips of the leaves it could be a ph fluctuation she may had had abit tioo much water. Try letting her dry out and only pouring water around the base of the plant when watering they dont need much at this stage so if you saturate the whole medium thats boud to be too much for hert and will result in slow stunted growth :) Best of luck anyway pal she looks healthy :)