she may be overfat for herself sounds like. don't pin point a goal weight...bodies don't work like that...not everyone can be a certain weight and still maintain a doable healthy lifestyle. and if u mean summer by the end of june, its unrealistic to shoot for 40 pounds... instead shoot for 20-25 if u want ot put a number on it. someone loosing it the healthy way can loose 1-5 pounds a week...the avg is 2 pounds a week for most...and sweetie she can have sweet foods. there are tons of recipes out there that are deserts and snacks that are perfectly acceptable to eat when on a healthier diet.
she need to eat healthy, veggies and fruits should be eaten first in a meal, then the lower calorie items like soups and natural starchy foods such as bananas and potatoes, then things like lean meats and grains should be eaten last....the idea is to fill up on the lower calorie better for u items so that by the time ur 60-75 percent filled up, u will eat less of the higher calorie items.
when exercising, she only needs 40 minutes to an hour or moderate to vigerous exercise a day, that means getting her heart rate up to id have to say 115 bpm...right in the middle of where she should be...she needs to aim for 103-124 when working out(u want ur heart rate in this target zone for 40 minutes minimum)...easy way to count is time 10 seconds, count ur pulse beats in ur neck or wrist with ur middle finger and pointer finger...multiply it by 6...its not really changing ur diet drastically, mroe of moderate and alter the things u need to alter...like soda to water/ carbonated flavored water (cascade ice is a great alternative to regular sodas if u just cant seem to give it up as well as propel fitness water) instead of a big chocolate chip cookie from the store, make some low calorie brownie cookies at home and just follow portion sizing instructions (the recepie is in better homes and gardens: Cook healthy today) again if a diet is as stricct as u think it has to be, the weight will come back because ur not modifying her lifestyle with better for u options that taste the same, ur changing it completely and still enforce the bad foods. if u want her to keep it off and be as healthy as she can be, u need to make it a lifestyle. something she can stay on her whole life with out feeling deprived.
that exercise would be fine that u list...cardio should take up 75 percent of that time...meaning running, swimming, biking for 45 minutes. strength should be the other 25 percent, in which u do stuff like crunches, squats, lunges, bicep curls...mucle helps in loosing weight because it speeds metabolism up. muscle is built differently on a girl than a boy so u and ur friend's sister wont end up looking very muscular, but more lean really...all those stars u see in hollywood do strengthening like it is a religion to keep theirselves looking toned and sleek...stretch after a work out only. flexability is a major part of being fit...at 14 milk is ur best friend, just switch to skim or 1 percent...the thing is, u stop building calcium on ur bones at a certain age to where it matters enough and u need a certain amount to grow being that ur young so that they stay strong...this is important because bones degenerate after u hit that age u stop building bones...which is in ur low 30's...and if u dont have enough built on those bones, u will eventually get broken bones or osteoperosis...which is painful to live with.
another thing, if u diet only, u wont keep the weight off. what u loose is a combination of muscle, fat and water when u diet only and loose weight...and remeber what i said before. muscle helps ur metabolism. when u loose muscle, u loose some of ur metabolism as well as the support muscle gives u that u need.