First the making of friends: I would suggest that you make "dates" with your daughter for the two of you to do something special together. Perhaps the two of you or your entire family could spend some time volunteering -- working for others. Encourage her to develop her talents or interests through clubs or community education. In other words, help her focus not on getting friends, but on being comfortable with herself. In doing all this she will make friends because she is an interesting and interested person.
Talk with her about what it was like for you to make friends: what you did, any problems you had with friends, and how you worked it out. Most of the time, young adolescents need to know that parents had to learn these skills too, and that it is possible to make new friends.
While you are helping your daughter be her own person, you can be working on the weight issue. This should be a family project, not her project. No dieting. No "You have to lose weight." First, get your family doctor to give your daughter a good physical exam and get his opinion if she is truly overweight. If he says she does need to lose weight, change what everyone in the family eats -- put the focus on eating healthy and wisely. Read or go to a nutritionist for advice on setting up an eating plan. Get active as a family: Take walks, bike rides, swim. Not only will activity burn calories, it will relieve stress for each of you, making everyone healthier -- more whole.
Feeling good about oneself includes mind, body, and spirit. When your daughter truly likes who she is, she will make friends.