A book about angels...it's difficult?

I know this is a horrible question, as it is difficult to answer because I cannot provide a lot of information. There was this story I read as a young teenager, about a girl who was hit by a car, died, and went to heaven. Then, to earn her wings, she was sent back to Earth in all different times to protect different people. She couldn't be seen by people on Earth, just other angels. I do not know what the title is, or any of the characters. I believe she may have been in love with another angel. The book covers were usually one colour - I distinctly remember orange and purple, and glittery. It is very teenager-ish and girly. I believe 'angels' or 'wings' may have been in the title. I know that this is a question maybe no one can answer as I don't have enough information. But thanks for reading and trying!