An interesting thread. I coach numerous females here in Australia and a few have achieved at a respectable level including one of my athletes placing top 50 at WXC in Denmark in 2019. I currently have a great group of young females distance and middle distance runners between 18-12 years of age that have run between 17:30's for 5k and as fast as sub 60 seconds for 400m. Currently I have a 13 year old that has run 3k XC in 10:30 and 5 other girls aged 12-13 that have run under 12 minutes with 2-3 days of training per week.
A few things that I try to stress with 14 year olds that are fairly new to the sport.
1. Find a group or squad with a knowledgeable coach
2. Make sure there is lots of easy running with bits of fast running on the flat and over hills.
3. Increase their volume slowly.
4. Most of their running needs to be on grass or dirt
5. During track season we only train once per week on the track.
6. When doing intervals include alternations. An example when running 400m's like you stated run it as 100m fast 200m easy 100m fast. You can do this for a variety of distances in training.
Now what does our training look like? Here is a sample week during our winter.
Monday OFF or other sports training
Tuesday 1500m warm up with dynamic drills and strides 3x4x 50-60m short hill sprints with jog down recovery 2 min btween sets finish with 1500m at 4:30k pace
Wednesday 30 minute easy run
Thursday 1k threshold which for your daughter would be around 4:45-5min k pace + 3-4x600m as 200 easy/100 fast 100m walk between efforts.
Friday oFF
Saturday 35-40 min run over hilly course
Sunday rest
Hopefully your daughter has a good coach and you are in an environment that is conducive to endurance training.
Good luck!