Hair grows from the root so if there are problems there it will not grow. Also if it's breaking of at the ends it will also look like it's not growing.
Post your daughter's régime and how you style it.
Also look at your daughter's diet and make sure it's balanced. Your daughter needs a diet low in processed foods and sugar/fructose. She needs to be eating meat including red meat, veg, fruit and some dairy plus get exercise every day. People including children don't need to eat as many carbohydrates such as potatoes and pasta as they think. What is healthy for your body is healthy for your hair.
Then look at how gently you and she are treating her hair. Things like no brushing/combing when dry, ensuring it's not rubbing clothing and pineappling at night/wearing a bonnet/scarf to bed will help decrease breakage. There are a lot of other little things that you could be doing like using the wrong hair ties that make a difference.
The only reason to use the oils is they help to seal in moisture there is absolutely no scientific proof they help hair growth by just application.
When I was a child mineral oil was used on my hair I didn't have hair growth problems until I was a teenage and anaemic due to heavy periods.