For your first question, I would urge you not to feed your chickens pasta very often. As much as you want to spoil them, it may end up hurting them in the long run. In the same way processed grains make humans fat, it will do the same to your chickens. As your chickens gain fat, it messes with their reproductive tract and can cause blocked eggs. There are other consequences, but that is the first that comes to mind. I don't see anything with giving them an occasional fruit or vegetable (with the obvious exclusions like green tomatoes and apple cores), I just caution with calorie dense, nutritionally lacking treats.
As for introducing a new bird to your flock, first and foremost it is recommended that you quarantine your new bird for several weeks to insure they don't have a disease. When you bring a new bird into your flock there are many aspects of this that place stress on the bird (imagine you being moved by yourself to a new town, lots of stress). Some birds have suppressed diseases that never emerge until put in a highly stressful position. To avoid a loss of your entire flock, keeping the new bird quarantined to allow for her to adjust to her new environment will ensure the safety of your flock. If you feel like skipping this step and hoping for the best, it may take several weeks or months for the new birds to accept her. That's just part of life. She may never be accepted, but chances are she'll work her way into the flock. You just have to be patient.