Brushing with a fluoridated toothpaste is important. I personally think switching to a another toothpaste does not make it more effective. Stick with ones that you enjoy the taste will make brushing more enjoyable.
Probably not your toothpaste (although some people are sensitive to sodium lauryl sulfate which is in most toothpastes). It could be from mouth breathing and the drying out of the mucosal tissue inside your cheeks.
Yes, you can use Sensodyne toothpaste, even if your teeth are not sensitive. It will not harm your teeth, nor make them sensitive. Thank you for your question.
Absolutely! You can think of toothpaste as a medicine. The longer that your teeth are exposed to it, the longer the medicinal effects of the toothpaste have to work. Leaving the Sensodyne on your teeth if perfectly fine :)
Swallowing toothpaste can cause stomach upset as well as other health issues if done consistently. If you notice her doing this often, switching to a non-fluoridated tooth paste would be a good idea.
Make sure you are brushing and flossing immediately after your meals. Plaque buildup mixed with saliva causes a hard substance (called calculus) to stick to the teeth. If plaque is not removed from the teeth in a timely manner, this is what happens. To fix this problem, it sounds like it's not as much about what you eat, but the timing of you brushing and flossing your teeth.
Stopping smoking will help prevent more stain from occurring, but your teeth won't get whiter just from quitting (you'll notice a TON of other health benefits from quitting though). If you quit and use a whitening toothpaste, white strips, or professional whitening, then your teeth will get white again. The catch with whitening is that you have to keep up with it. Dark drinks (ie. wine, soda ...