:grouphug:This is what I would do:
Give her as much one-to-one attention, love, cuddles and time as you possibly can, forcing yourself to not react when she irritates you. If you feel so irritated that you feel you are about to react it is time to switch the activity you are involved in. E.g. when you can't take it any more playing the Wii, say "Let's play Hide-and-Seek" and have as much fun as you can doing that. But keep yourself completely engaged with her absolutely as much as possible.
Something my little ones love from time to time is cuddling up while I tell them the story of when they were born with as many details as you can think of. They know the stories very well, how I loved and wanted each one, how happy I felt when I first saw them, what we did when we got them home from the hospital for the first time . . . and so on. Also they like to hear the stories of how their names were chosen and the meanings of their names. They like to hear the stories of people who had the same names and how good, brave or whatever these people were.
We have Bible stories every evening and keep it a fun, positive, calm and loving event. We also have Bible studies every morning, again in an uplifting, joyful, loving atmosphere. We pray every morning for Holy Spirit to display the Fruitage of the Spirit in our dealings with one another during the day, emphasizing love, joy, kindness and patience.
When you are reading to her, try giving her something else to do at the same time. My 14yo, 9yo and 5yo like to sew while I read. They sometimes draw, colour, play with lego or practice handwriting while I read.
She can help you as you do the housework and the cooking. Make it a treat for her to help you. Do housework for a set time then promise you will sit together with a cup of hot chocolate or something and chat. Or have a girly makeover and manicure, or do her hair in a special way.
If you feel it would cause too much difficultly to stop her watching certain shows, you could sit and watch them together, pausing the show if possible to discuss issues and why you expect better/different behaviour from your children. You may find after watching several episodes with your full attention that you will have a lot to discuss with both your girls.
I have a different take on the breakfast issue. If she is used to you preparing food for her it may not have occurred to her that she could help herself. I can sympathize with an eight year old being hungry at that time of the morning and feeling that she must be fed immediately. Maybe you could have a chat with her and give her some strategies for dealing with this - explain in advance what food she can help herself to if she gets up before you.
At a separate time I'd have a gentle chat about respect within the family and appropriate speech. It's simply not her fault if she is copying inappropriate speech from TV shows you allow her to watch. (I'm not suggesting it is your fault either, I think it's shocking the kind of language the children use towards each other and their parents/teachers and so on on many of these show which are targeted at young children.)
I think she needs lots and lots and lots of reassurance that she IS good, that God loves her and thinks she is good and that you love her and think she is good. Not just verbal assurance but a general feeling that you trust that she is good and will do the right thing and that when she gets things wrong you understand she made a mistake and that you forgive her and love her.
Sometimes it can be hard for a younger sibling to cope with having a 'good' older sibling to live up to. We just read the part in 'Little House in the Big Woods' where Laura slaps Mary after a long build up of jealousy. I think a lot of younger siblings could identify with Laura's feelings there. A younger sibling has a lot to deal with one way or another and may need years of reassurance that they are just as loved and valued as their 'superior' older sibling. Even if you are absolutely certain that you never hint that your older daughter is in any way better than your 8yo, she will be noticing for herself the way things are.
:grouphug: I hope you can find something of some use to you in this rambling epic.