Once she gets a feel for how many calories she’s eating on a typical day, and how many calories are in the foods she eats all the time, it gets a lot easier.
I kept a food log on fitday at first, then before long I knew exactly what was in everything I eat regularly.
Another idea. You’ve heard of the 1 gram of protein per pound as a recommendation for people lifting weights. Just track protein, then try to make healthy food choices, and track total calories. In other words, hit protein targets, don’t eat too much, eat healthfully but let the carbs and fats fall where they may.
You know you’re eating too much when you’re scale weight isn’t moving or your scale weight is going upward. I’ve done this many times. It’s not the the way to go if she were trying to get stage-lean, but if she just wants to get back into her pants, it should do the trick. 
It’s an easy way to get started. She can always start dialing it in more if this approach stalls.