I have a friend who is VERY big.. 26yo, f, 5'9", 335 lbs... help.?

Can anyone give some advice as to how many calories she should be taking in to lose weight? She has been going to the gym for about a month or two and has dropped 30lbs, which is great, but I'd really like to see more results. She doesn't really understand the concept of "healthy eating" yet, but I'm working hard on that. She's way too young to be this big, so any (empowering) advice would be great. Thank you. :)