Practice makes perfect!
I had to start doing Muffin years ago. She's gone to Rainbow Bridge now. She much preferred me doing it, though...even if she was my first victim!
I have a little girl now that is 4 months old today. I haven't done her myself yet, but if she calms down someday I'll probably do her, too. All I can tell you is try if you're daring enough.
I'm just kidding! Actually, whether you use shears or scissors depends on the cut you want to give her. You can use scissors if you intend to maintain a long cut. If you want her hair shorter, you can use shears with the whatchamacallit on the end (help me out guys) that will give you the length you want. She really is sweet and oh so cute!