It is normal for kids to stretch the truth or test out fibbing right now. The big thing is to let her know the difference and give her a chance to redeem herself. WHen she lies and you know she did ask her nicely "well, I want you to think hard, is that what happened really?", giving her a chance to process the truth. If she still lies, then have consequences. It is a normal phase, you just have to really nip it in the bud so it is just a phase.
Both of my kids would fess up if I gave them a chance to not being angry at first but tell me the truth.
Then I had this rule, "you may get into trouble for the bad deed, however if you lie about it the consequences are going to be worse"..I stayed true to my word, and it worked like a charm! Both know that the truth may get them in trouble but if they lie it is way worse!
Be consistent, but give her a chance to fess up first.
Then explain "we do not lie, you need to tell us the truth so we can believe you". Another thing I did with my daughter was if she told me the truth after lying a bunch I told her "well I have a hard time believing it is the truth you have lied so much"...she was older then but it worked in her brain to realize if she lies, then tells me the truth about something I am going to have a hard time.
A boy I watch started lying to me, I explained that if he got hurt and I asked how, it was so very important I know the truth and I won't tolerate him lying to me. Explaining why the truth is important. He had to sit in time out then I would have a talk about being honest.
Takes time but she is fine, it is normal and all kids go through this phase.
If you think she is having a hard time knowing what is a lie and the truth give her examples. Like show her an apple and say "this apple is blue"...see what she says, then point out that would be telling her a lie, that it is really red....easy stuff to use as examples.