yeah thats a nitrogen deficiency. Quick tip, deficiencies start from the bottom and work their way up, over fertilization will start near the top with the newer growth. What type of soil are you in? Miracle Gro? Miracle Gro nutrient will work. Id suggest if your going to use nutes from a walmart or something like that you go with something like Expert Gardener All Purpose, something for fruits and vegetables.
Remember when your vegging, you want your N-P-K values to look something like this 2-1-1 (they vary of course) those numbers can be higher but you want the N-Nitrogen to be higher in value. When you get into Flowering you want 1-2-1 or 1-2-2 for example. You want the Phosphorus levels to be higher than the nitrogen. If I had to make a recommendation for nutrients you would order online, Id go with blueplanetnutrients.com you can get the 3 part system in quart size containers plus a quart of their bloom booster for about 40 bucks which includes the shipping in that cost. The shipping is very fast and the nutrients are designed with MJ in mind.
Be sure your watering the pot until you see water running out of the bottom. Remember you can't over water in one session so don't worry about drowning her that way. Water good, wait a few days until the pot gets good and light, water again. Right now the miracle gro will work until you can get something better. Looking at your pics I think whatever the recommended dosage on the package says will help her bounce back. Wait a few days since you watered recently, see how she looks. If you see no improvement just add another normal dosage to your watering.