At best, that is a small cage. I honestly would not house a healthy conure, let alone a cockatiel, in a cage that size... but that's me! I would view that cage as nothing more than a sleep cage at best. (I disagree with the cage sizes recommended for birds)
Can you get her a larger cage? Nothing smaller than a 32x23 cage, but I'd recommend 30x30 or larger. If you have the space for it, a 40x30 or larger would be fantastic! (one of the reasons why I don't own a large parrot is because I don't have the space for a large cage - and I've got a walk in aviary for my little birds!
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Ideally, she should have a minimum of 6 toys, but more is preferred. This is partly why a larger cage would be beneficial! More toys! And more perches!
Have you tried feeding her nuts? Nuts should be a part of her diet. Walnuts at least... perhaps some macadamia nuts, almonds, pistachios, etc. Pine nuts may also be enjoyed. Here's some ideas on getting her to eat a more varied diet.
A healthy parrot starts with a healthy diet. Although the perfect diet is controversial, many parrot enthusiasts and experts agree on one thing; a seed only diet is a diet that is lacking in essential nutrients, vitamins and minerals. Studies have shown that adding fresh foods and pellets to a...
forums.avianavenue.com
Does she may have a play stand or gym she can go on away from the cage?
You can either buy or make her foraging toys. There are toys with slats and holes drilled into them that you can stuff food into. You can cover the food dish with a paper towel (with a large hole initially) so she has to rip through the towel to get to the food. You can wrap food up into mini cupcake holders. You can fill a container up with some smooth rocks (too larger to eat) and mix food into that.
As far as training goes.... there's a lot of resources I've gathered in this thread.
Someone recently told me that there was only one trainer on the internet that had free training advice. This is, quite simply, false. This “trainer” they spoke of is an amateur that has taken advice from salesmen who market themselves as bird trainers. Not to say that they don't enjoy helping...
forums.avianavenue.com
It's a lot to take in, and I'm sorry you are put in this position. I don't know how old you are, so I don't know what you can afford to get. You can always look at getting used cages and disinfecting them before use. Of course, you need to be careful that the cages are 'bird safe'. There are many cages out there that are not safe for birds. Those with scroll work, "v" shaped wires, open top cages, "v" shaped legs, etc.