Hello, sorry for the delay. I just now checked in.
Sometimes certain bird will hold their poop if they are reluctant to soil their cage, or if they were "roilet trained" to poop on command.
It's not horribly dangerous but would be better for a number of reasons if she just did it normal style.
You might try toilet training by saying "poop" or whatever coimmand you want, when you first come home, so she associates the act of defecation with the word. Then several times a day, when you can, do this while she is on your finger in the cage. That way she will learn it is OK to poop in there.
Hopefully this is just a habit, but it can be a sign of a problem. Some female cockatiels, even very young ones, can have calcium issues. One thing that happens is poops can be large and in frequent. Having her on a good diet, a 12-14 hour dark, quiet uninterrupted sleep cycle (at night), plenty of exercise and some outdoor time (safe and secure of course) can help.
They can have GI infections and parasites, both are easily discover by routine poop sample.
Making certain she eats a lot of dark leafy greens will improve GI function and take the GI back to a more normal state.
If she has not had a routine health exam and basic lab work by a really good bird doctor, she needs to have that done ASAP.
I really must stress that you need a bird-experienced person, and not just a vet who advertises that they care for birds.
You need to take your bird to see an avian-experienced veterinarian ASAP for complete examination, diagnosis and appropriate treatment. Check
https://aav.site-ym.com/?page=basiccare click on "find a vet"
great tips for egg-laying and/or female cockatiel issues:
Birds should be on a high-quality, preferably prescription, pelleted diet: I prefer High-potency Harrison's
In addition, they should be offered dark leafy greens, cooked sweet potatoes, yams, squash, pumpkin; entire (tops and bottoms) fresh carrots and so forth. No seeds (and that means a mix, or millet, or sprays, etc. etc.) and only healthy, low-fat high fiber people food. A dietary change should be closely monitored and supervised by your avian vet.
Birds should get 12-14 hours dark, quiet, uninterrupted sleep at night. Any less and they can suffer from sleep deprivation and associated illnesses. They should be covered or their cage placed in a dark room that is not used after they go to bed.
The cage material should be cleaned everyday, and twice a day if the bird is really messy. Paper towels, newspaper, bath towels are ok. Never use corn cob, sawdust, wood chips, or walnut shell.
Food and water dishes should be cleaned and changed daily. Keep one set cleaned while the other is in use.
Fresh, perishable food should be placed in separate food bowls. Remove fresh food from the cage after a couple of hours to avoid spoilage.
Change cage papers daily, and clean the grate and tray weekly.
Clean food debris or droppings from toys and perches as needed (which can be as often as once a day).
Grit is not necessary for birds, and will cause digestive problems and death. The best sources of minerals (and vitamins) are leafy greens. Never give grit, gravel sandpaper or cement perches. A bird will eat those to excess when it is not feeling well or if there is a nutritional deficiency. They do not need it at all (an old myth from the poultry days, even poultry do not need it). It can cause an impaction and lead to serious or fatal consequences.