The issue of whether an athlete should participate in a sport is up to the athlete and his/her doctor. If a child has a doctor's note saying she is fit to play, then no coach or organization should overrule their decision. Anything else, and you have male coaches subjugating females for being female.
E.g., what does "showing" mean? Does that mean an overweight athlete can pitch into her 3rd trimester while the underweight athlete has to quit after one month? It is totally, completely arbitrary.
Whether she can "participate in a sport" may be up to her, her parents and her doctor. However, whether she (AT AGE 14) can participate in a game on my team is my call. Had this happen on 8th grade school team - 3 years ago, she quit - it worked itself out. However, we are forgetting one aspect of this conversation - it is ILLEGAL for a 14yoa to engage in the acts that got her that way. If you catch a 14yoa using meth, shoplifting, stealing a car on your team, cheating in school - how do you handle that? If she is the victim of a crime - I may handle it differently - hope I never have to make that call.
There are consequences for your actions and if a kid on my team shows up pregnant - I'm afraid we ask her to sit out a season.