How should I handle my 12year old daughter?

She wants the following for Christmas:
Michael kors purse and watch, a new Iphone, Victoria secret clothes, and a hollister $150 gift card. She is desperate to be popular and is trying out for cheer in April of 2018 but she can't do any flips, she can't jump, she has no friends at school, and she is not flexible. She is so desperate to be popular in school that she wants to copy the cheerleaders and she ditched her best friend who is on the cross country team to attempt to fit in and I really do not like her behavior. A year ago she wanted to be a softball player but she did not try out for the school team because it was not "cool enough." She is very good at softball and cross country. She also has been defiant at home by not doing her chores and she is failing pre algebra. Should I ground her?

Let's pretend this is true, shall we?

You don't sound like a good parent at all.

Take a class and get better.

Here's the skinny:
you don't have a 12 year old daughter,
you made this up,
you have posted this before,
if any of this was true - you made the monster, live with it.

Grounding won't help. By grounding her you will simply paint yourself as a monster of a parent who doesn't want her to succeed in life and be happy and popular. And there's no point in that, because she will not listen to you, but will simply rebel. No. What you want is to help her achieve what she wants. First you establish how much you can spend on her for christmas. Then you compromise with her that if she manages to do a full cheerleading routine by christmas, Santa will come, so to speak. On top of that, chores, and grades have to rise.

Taking away her phone should work wonders.

Ground her? She has taken a left turn and need to be brought back to the right path. You should have acted as soon as you saw it starting as opposed to now, where it may be too late to alter her course. Good luck to you grandma. Because that is the direction you are headed in.

Are you seriously seeking parenting advice on ya? Lol that poor girl doesn't have a fighting chance with a nit wit like you as a "parent".

As the parent you are responsible to take the lead. That means teaching her values, if you don't the ones she picks up will be what she sees in her friends, in movies, advertising, TV etc. And those seem to be how she is acting.
Parents need to set limits and reinforce them with appropriate punishments when the limits are exceeded.
They model appropriate behavior.
They teach values and provide opportunities to learn more about what the family values at places like church and Bible study.

I'm sorry people are being so awful with your question. I appreciate you are seeking help because no one has this parenting thing all figured out. Thank you for trying to do something rather than ignoring the behavior.
I would suggest having a sit down discussion with her and not agreeing to any (or very few) of her requests for Christmas. She's valuing popularity over actual relationships and thinks that "money" is the answer. Is there someone she thinks is really "cool" in your family or that she looks up too? I had a much older sister who was not raised with me. Any time I got out of hand, my Parents would ask her to take me to lunch and chat. This worked wonders because it came from my "cool" sister. Take her to talk to the cheer coach about what behaviors are expected from a squad member. Grades, working with others, hard work and being an example in your school are key elements and if she's looking to try out, she should start now. Just some suggestions, best of luck.

Troll

Well I had issues similar to this when I was 11 or 12, first year of middle school was bad. I'm a guy though so I didn't go through anything completely similar. I
wouldn't completely give in but I also wouldn't ground her or punish her too much. I didn't know who I could talk to and that was my problem, she shouldn't look to be popular but accepted and appreciated. Meeting people is hard though, I would have her join a club she liked so she can meet people who share an interest through the club and eventually introduce you to other people. It also helps to find something you can do that other people enjoy, for me that was cracking jokes. I don't think you should buy all that stuff she named, I think that'll make her liked for the wrong reason, but if she wants to buy that stuff because she likes it that would be better.