Those Fiesta type mixes promote selective feeding. They're very unlikely to eat everything in the mix. Seed mix on a whole isn't a very healthy diet - I'd look into trying to transition her to a good quality pellet.
Cockatiels being granivores still do well with seeds in their diet, though. I personally make a homemade mix that I can feed dry OR sprout with beans and such added. If you'd rather a commercial mix, some good quality ones are Higgins (Safflower Gold or Mayan Harvest Yucatan), Volkman (Super Cockatiel, No Sun), or Versele-Laga (Loro Parque Australian).