Hi,
The best thing to do is take her to an Avian Vet as soon as possible. It sounds like she could be egg bound, but there could be something else going on. She shouldn’t be lethargic, even when about to lay an egg. If you aren’t confident with the vet you have gone to, it is perfectly reasonable to seek a second opinion.
As for discouraging egg laying, it will be harder with a male in the cage. A female cockatiel can have her hormones triggered just by the sound of her mate. Even if they aren’t bonded, he’s a male and that can trigger egg laying. Besides separating them, which may or may not help, especially if he calls to her, there are changes you can make that may help. If the changes do not work, hormone treatments work well with cockatiels, especially the implant.
Keep in mind that to lay eggs, she needs longer daylight, warmer weather, abundant food, and a quiet, private environment. The goal is to reverse these conditions.
Limit her light to 8-10 hours by covering the cage early each evening
Do not give her anything to use as a nest – no bird huts or tents, no box, bowl, etc. If she decides to sit in a food bowl, remove it and replace with smaller cups.
Do not give her anything to shred such as paper or cardboard.
Rearrange the toys in the cage frequently.
Move the cage to a different place in the room. Move the cage about once a week, or whenever she shows signs of nesting – settling on the cage floor for example. This disrupts her idea of having a stable place to lay eggs and raise chicks.
If you feed a lot of fresh foods, stop offering any for a couple of weeks, and then only offer them in small amounts about 2 or 3 times a week. You can resume normal feeding later when the birds aren’t being hormonal.
If she is let out of the cage, do not let her get in any dark cozy places and don’t give her free roam.
When you handle her, limit any petting to only the head and neck – do not pet a bird on the body. Only a bonded mate is allowed to groom the body. We can’t be a mate, so touching the body is off limits.
If there is no metal floor grate, then do not use any bedding or paper in the cage tray – leave it bare and clean it daily.
Thank you for asking Lafeber,
Brenda