Amy, Get a handle on your daughter now. If YOU think she's spoiled, others will really believe her to be a brat. Most kids do go through phases of rebellion, my son (9 now) included.
Find out what she values most and physically take it away for infractions. Be stern, enforce after first warning. If the offenses continue, warn her she'll be donating it to someone else who can aprpeciate it. Then make her go with you to donate to a charity or someone else who can appreciate it, and if she has a few items of a kind, make her pick her favorite and donate it. While it may seem harsh, it'll reinforce your discipline and that you won't put up with bad behavior, it can also give her a glimpse of how fortuante she is and others aren't. She'll figure out real quick while she doesn't "have to have" those things, it sure is nice to afford them. And should help her better appreciate them.
Take her to the grocery store or other place when you shop and have her help, shop for less expensive items in some things and get her invovled in checking. make her do chores and award a certain dollar amount for it weekly or monthly, for items she wants. Make her know dollar amount of toy or clothing, movie, etc... so she'll know what she's working for, then help her figure how long she's going to have to work for it. Not only is it good discipline it teaches work ethic and mathematics.
Or for bad behavior, especially over things or toward others, make her do "community service" if there's an organization around that helps moms and children, the elderly, or something she will understand. Take her to a soup kitchen and make her help. She can stock napkins, utensils, carry small stuff, be a door greeter, help pick up trays or trash, etc.... if you go to church and they do charitable acts, get her involved. Talk to her teacher and find out other opportunities. There' always something she can do. Take her to other sections of town and let her see differences in living conditions. etc....
Make her write 10-25 sentences that she won't repeat the bad behavior, or a paragraph as to the problem and how she's going to fix it. Seems basic from way back, but if they have to write a page full of sentences, esp. if they don't like to write, it'll pay off in spades very quickly. If she balks at this, add 10-25 lines per repeat offense, or even 50 for really bad behaving.
As far as entitled, what kind of friends is she traveling with? Are they too possession obssessed? If so, this could become a problem. Talk to her about it. Others may have things, but are they happy? Instill that those who have do for others, not themselves. When she feels "entitled" call her on it, explain that you aren't legally obllgated to do more for her than clothe and feed her and put a roof over her head. DO NOT give in. Also, if she likes going or participating in activities outside the home, take 'em away too. When finances are tight, explain you'd like to do for her but as a family, you just can't afford it. Would she rather have food to eat and shoes on her feet, a place to live, or does she want that thing. Let her know priorities come first or you end up on the street.
Is she acting this way just at home or in public too? Sometimes they're just tired and cranky from being shut up inside all day in a structured environment like school.
Hang in there. Eventually she'll get the message. Just be firm and don't give in (I know, not always easy, but in the long run, well worth it).