Thanks for asking the query,
Bleeding and swollen gums
occurs due to poor oral hygiene
due to crowded teeth, due to errupting permanent teeth
and calculus deposition, nutritional deficiencies.
If your daughter is traumatising her gums while flossing, you can quit flossing for 4-5 days till the gums heal. Select a proper toothbrush for her, you can go for a soft bristle toothbrush and brush the teeth in circular motion and for gums use flicking movements without any pressure.
You can visit to an Orthodontist and get a checkup done, treatment of malaligned teeth is necessary.
Swollen gums can be due to errupting permanent teeth.
Meanwhile go for a symptomatic treatment of complete mouth scaling and polishing.
Use antiseptic mouthwash gargles twice daily.
Maintain a good oral hygiene.
Take complete balanced diet.
Give her plenty of drinks, juices and water and keep her body hydrated.
Hope this helps out.