So your dd is lying and you are going along with it? What kind of life lesson is that.
I also might suggest that if your daughter lies to her dad in favour of going out with friends you should be stopping her seeing her friends on those weekends...
Perhaps you should sit down and explain that as she's getting older now she does of course have other things she'd like to do, and friends she wants to see, but it is important she see her dad too. So how about suggesting that she sees him slightly less often but that when she does they plan on something to do. Or sugesting that dad might like to facilitate the friendships and that she can phone her friends from his, or won't miss out on cinema shopping etc as dad will take her to them...
And when i say sit down and discuss i mean with your daughter but also her dad.
If her dad went along with your dd dilberately lying to you would you be happy? Or if he kept information from you that you should be aware of would that be ok with you? And yes you are going along with it despite you saying you won't lie if asked. You are not addressing it so are party to the lies imo. If she can make up eloborate lies like this to him what's stopping her doing the same with you? Are you sure she's seeing friends and it's not a web of lies so she can see a boy friend instead for example?
Speak to her dad and explain that part of your dd's fear on telling him is because she is worried about his raction and so he must try not to be angry about it with her and that will inpact negatively and could result in her refusing to see him all together.
Then explain what is going on and make a suggestion that he see her slightly less but that you will insist that she does goes at these times and ask him to plan things with her to give her something exciting to look forward to and more insterested in spending time with him.
And most importantlly if your daughter lies don't reward her by allowing her the time to hang out with her friends that she has lied to get!