I used to teach kids and from experience they want to feel good about what they're doing and don't want to get overwhelmed. It would help her if you first tell her what is good about the drawing. be specific. let's say she shows good proportions or she drew the eye well.
then focus on only 1 area of improvement and make the steps clear and doable. 1 week in the life of an 11-year-old is a long time! so better not give her homework or an assignment that takes more than 1 day. you can email on a weekly basis but let the assignments be as short as possible for her to see improvement quickly. "You drew the eye really well, now let's do the nose, watch this video and copy it then show me". the video shouldn't be too long either but I think at 11, she can handle up to 20 minutes if she's enthusiastic about learning.
when she shows you her work next time praise it, and be specific about what improved then give her a new assignment.
if you want you can tell her what the main goal of your assignments is. "your skill at drawing portraits will improve a lot in 1 month" or "your ability to see and draw form will improve in a month". and do a comparison of before and after to show her she's really improving. and keep in mind that you're a professional illustrator with years of experience, so don't hold her to those high standards.
oh yes and if possible, have her try different mediums, it's makes learning more fun especially when there's repetition.
pencil, colored pencils, markers...etc