I read a great article about how to motivate your kids a couple weeks ago- Stop the Stalling: How to Help Kids Stop Wasting Time, you can access it at the link below
When I was trying to find that one, I also stumbled across another article titled: How to Motivate your musical child, from Parenting, which offered the following tips:
1. Sit nearby. Even if it's just for several short sessions per week, you can limit distractions by staying close by while he plays.
2. Keep the instrument handy and in plain view. Seeing it each day will remind him to practice, and he might be more likely to pick it up if it's right there.
3. Build practice time into his daily activities. Setting aside time before leaving for school or right after dinner each day will help your kid remember to make rehearsing routine.
4. Hold "concerts." Have your child perform for you and your family on a regular basis. Tell him specific things you love about his playing, and keep yourself up-to-date with what he's working on so you can comment on improvements at each show."
I like the fourth suggestion the best; often it's hard to recognize our own accomplishments when it just feels like frustration but we don't feel like we're getting any better. A concert for the family will give her something to look forward to and a chance for her to receive recognition for all of her hard work- giving her (only) complements afterward will really help her feel like progress is inevitable:)
I really wish that I had more guidance to pursue my musical interests as a child- it can be discouraging but a very rewarding form of expression when you get good at it.
Definetly make it enjoyable by breaking it down; ie. ten mins. a day on two different songs or whatever will prevent burn-out.
Good luck to both of you.