My daughter swallowed a very very tiny magnets from the tip of a pen, should I be worried?

See below. If she swallowed more than one magnet, she should be seen. They can stick to each other in the intestinal tract, and cause problems.
One caution. In your question you mention "magnets". One magnet should not be a problem, but more than one can be by sticking together in different loops of bowel and causing a perforation.. Howevever this usually occurs with more powerful button magnets and would be unlikely with tiny weaker magnets from a pen.
Swallow foreign body. This should pass without problems. An xray will make sure the foreign body (fb) didnt get aspirated into the lungs. If the fb was swallowed normally without choking or coughing then it willl pass. Tell primary doctor. If any fever or pain, go to er or doctor immdiately.