Prism99 gave you great advice.
Are they a bush or staking variety of tomato? Bush ones should have blooms and be setting fruit. Staking ones will be leggier than bush ones, but should have flowers.
Did she use potting soil or garden soil in the pots?
Yellowing leaves indicates a lack of food, so yes feed them according to the fertilizer package directions. Does she have a pan under the buckets to hold the water? If the pots or really dry the water may run right through and not be absorbed. Putting a pot pan underneath makes sure the soil has time to absorb some of the water.
I have about 5 varieties of tomatoes on my deck. The temps on my deck get up to 40 degrees C or 104 F. It is hot and dry, we do not have high humidity. I have to water every morning and really give the plants a good soaking (until I see water in the pans). I started harvesting cherry tomatoes last week. Sometimes I have to water at night too, but it best for the plants to be watered in the morning. As well avoid getting the leaves wet when watering.
I use Miracle Grow tomato food every couple of weeks. I do not read the label on the container.