I also struggle with capturing a person's likeness... Especially if it is someone I know. (Which can make you feel really dumb since you've known and seen this person for so long!) What typically helps me when looking at the proportions of a figure is to look at one thing's relation to another. For example, look at your friend's left eye(her left). Draw a straight line from the corner of the eye down to where her neck starts. In your sketch, he neck starts directly below the start of her left brow. I hope this kinda trick helps! It's a little tedious to get into the habit of looking at limbs or facial features in relation to one another so don't feel bad if you have to remind yourself to look. Even though I know this trick, I still have to remind myself a lot of the time too. (Hope your friend has an awesome birthday!)