There's a guy called countschlick on deviantart who's done guides for all the Mane 6 that are very good.
Here's his guide for Rainbow Dash. You could use it for Lyra.
Linking because file size.http://countschlick.deviantart.com/art/Rainbow-Dash-Hair-Tutorial-313952831
It's a good idea to experiment with the spacers before cutting. You could skip second spacer on her bangs. It will make it look less unkempt.
Lyras hair also curls up a bit in the back, you could check the Rarity guide, which goes into curling in depth. You'd have the curl start a bit closer to the head for Lyra and cut cut off most of the curl so the hair doesn't make a full circle.
The horn is going to be a pain in the ass of course. You'll just have to deal with it.