At younger ages like 3 to 5 years of age most children do not have a comprehension of lying and it truly is innocent. They tell you what they believe you want to hear because they want to please you which is very different than being deceptive.
Older children usually lie because they don't trust you with the truth. This does not mean it is your fault; it could be as simple as she doesn't trust you to not punish her for telling the truth.
You might try not believing anything she tells you. If she says the sky is blue, look out the window and confirm it. If she says her socks match lift her pant legs to check. If she says it is 4:00pm check your watch or phone to make sure. Let her know how it would feel to not believe anything she says. I had a foster daughter who lied a lot. Most of the time it was brought on because she was trying to manipulate me, her teacher, or her brother. She also lied because she knew what the consequences were for breaking the house rules and she didn't want to follow them rules but she didn't want to pay the consequences either. She didn't trust me to not punish her so she lied. Initially, she didn't but when she saw how compassionate I was towards her brother regarding his issues post truamatic stress disorder (different issues altogether) she started taking advantage. Initially, she would lie and say her brother did things. Eventually, he started standing up for himself when he learned I would not beat the daylights out of either of them. Apparently, he would take the heat from their birth father for his sister to protect her. After a while, he figured out that the worst thing that would happen to either of them is to go to bed early or a toy would be taken away for a week. I guess he figured she could handle that kind of punishment. He wasn't taking her consequences anymore. She started having to pay the consequences for her own actions and she was being punished for the first time in her life. Up until that point everyone thought she was a perfect angel. However, it was not the case at all. She did not like being held to the same standards as her brother so she started lying about everything. Her brother did a lot (I mean a LOT) of things wrong but he always owned up to his actions and never lied about his behaviors. She started off blaming him for her actions and eventually, he started denying the things she said he did. Him I trusted to tell the truth her, I did not. She HATED it. She would turn beet red with anger and frustration because I could not believe her whereas everyone else always believed her even when she lied. Once her brother started standing up for himself, I started finding out all kinds of things she was lying about. The more I caught her in her lies the angrier she got. All in all it was a habit that we broke in about 3-4 months but it took constant vigilence and I could not let her get a pay off for any lie no matter how exhausted I was of monitoring her every move.
Monitor everything your daughter says and do not allow her to have a pay off for lying. She is getting a pay off somewhere.
Good Luck. It is not an easy habit to break. I am glad that problem is behind me and don't envy you in having to deal with it. My daughter is only 5 and does not lie at all. My foster daughter was 8 when she started lying. Maybe it is a phase that some 8 year olds go through.