I also don't recommend flat ironing often. I usually only do it once a month at most. Going CG (no sulfates and no silicones) has made my hair healthier and more manageable. Encourage her to embrace her waves rather than fighting them.
Here's just a few tips...
For tangles: use a conditioner with a lot of slip (I've heard Garnier Fructis Sleek & Shine is good; I use Tresemme Naturals) and use a wide tooth comb with the conditioner in the shower to remove tangles.
For frizz reduction: don't touch hair while it's drying, use an old t-shirt or microfiber towel to dry hair
Hope this helps!
Wave Pattern: 2A
Hair Properties: Normal/Low Porosity, Medium Density, Medium Texture w/Fine Straight Underlayer
Co-wash: Suave Naturals, Cure Care
Low-poo: Renpure Brazilian Keratin
Rinse Out & Leave In: Tresemme Naturals
Gel: LA Looks Mega Mega Hold Gel, Garnier Fructis Spray Gel