How about letting her know that you love her very much and giving her 60 days notice to find her own place? She is 21, working, and has a car. She is not in school and isn't married or a mom yet... this is a great time for her to be on her own. If you can come across like this isn't punishment... it's just time for her to move out. (She can come over for dinner on Sunday or whatever is a weekly family tradition) Before you give her the push out of the nest, make sure she knows you will not bail her out if she is arrested for stealing or any kind of fraud (lying). [Do not bail her out for any reason.]
You can be genuinely empathetic about how sorry you are that she is struggling with her integrity and still give her notice to move out.
Why? You have little children in the house watching the lying merry-go-round and this isn't good for them- or you. Sounds like the little ones still have character that can be shaped at home.
It's more stressful for you when you can watch your kid "crash and burn." I think you need the distance in this case to let her make her choices and the consequences occur. Step out of the way and let God deal with her directly. You can inflict punishment, but consequences are better teachers. Since you've raised her with godly values, she will most likely return to her core faith after some rebellion. (I rebelled in college, not high school. It may be rebellion since she doesn't seem to lie all the time)
I have a family member who doesn't act responsibly unless she has to. By that I mean, if she lives with my mom, than she expects mom to babysit her kids, cook, do laundry, loan money when she is broke, etc.... and, yes, she works and pays for her own car. (She's on her own now and is doing better than ever.) Your daughter may do the irresponsibility with lying,buying, stealing because she knows she has a safety net.
You can offer to pay for counseling since she will be on her own and might not be able to afford it. You can also offer to find her a budget counselor in case that is more of her problem. Brenda Haley in Corinth/Denton is awesome, but I know there are several great ministries for this. (Just remember you can't force her to go to either counselor... only invite her as a gesture of your genuine concern for her character and well-being.)
Your are not giving up on her by having her move out. You are sending the message that you find this behavior so alarming that she needs to be out of the house. You are sending the message that you will protect your children from her since it is currently necessary. You are sending the message that you love her and want her to get counseling.
You can read more about what I mean in "Parenting with Love and Logic".