How do I seduce her?

The only way you can possibly do this and have any chance of success is to get her to seduce you. You have to show a little interest, but just a little. Don't escalate. If she wants you, make her do the work. If she does the work and really believes that she seduced you then she might not tell. If she does tell your daughter, your life will blow up very badly.

That means that you have to play hard to get. But you do have to show just a little bit of initial interest to get her to thinking about it. If she thinks that she seduced you, she's not likely to go mentioning it to your daughter because it would make her look like a slut to your daughter.

Start being very friendly and cuddling her a lot then move onto patting her bum and rubbing over her breasts when you cuddle, if your female it should be so very easy, buy them both a new sexy pantie and bra set and ensure they model for you, daughter first then give her a giant hug then her friend should expect the same so you are nearly there, please let us know how you go

Umm how about you try thinking with your upper head (the one above your shoulders) and don't fuck with a friend's daughter? Asshole.

You're assuming I'm male...

It can be metaphoric if you're not male. The sentiment still stands. Don't fuck with a friend's kid - even if they're legal age.

Spend time around her, learn about what she and her age level like, and talk to her about it..Make it a thing. When you get closer b/c of it, start hinting at more, just between the two of you..Hug her more often, get physical with her. Get your hands on her often.. She'll get the message.