battery life is good. Everyday I go home at around 7pm my battery life will be between 40-60%. wifi on during working hours + some data connection.

Hi, if it helps - I use my s3 moderately, calling, sms, email and occasional browsing and camera.
Usually I still have over 50% by evening, and it will last me till I plug in to recharge before going to bed.

It also helps a lot if you have a spare charger in the office or the car. A short top-up charge extends the usage life significantly!

I am on custom rom with the latest firmware. The latest firmware really give a lot of improvement to the battery life. So far I don't have any of the problem you mention there. If she only use whatapps and facebook, should be able to last her until late night. So far, I can use for 1 days and 20 hours with mostly wifi, some data and some game. Previously, I use it for very minimal usage (wifi on for 2 hours at night only), it can last me for 4 days + and that was with the old firmware. I believe with this new firmware it will last even longer.

That's all the information I can give you