Is the questioner considered to be among those who publicly commit the sin of zina (fornication/adultery) for fabricating a false story about committing it and suffering a pregnancy in order to warn her friend, and does she bear the sin of her friend who later fell into it, and is there expiation for that, and what is the solution for her to purify herself from this sin, knowing that she fears informing her married friend about what happened out of fear of problems?

It is not permissible for a Muslim to disclose a sin unless there is a valid reason, such as seeking a fatwa, offering advice, or confessing to the ruler. However, since you were acting on an interpretation (ta'awwul) when you informed that woman of your situation, we hope that there is no sin upon you. You are not responsible for what that woman did because she brought it upon herself, and you have no part in her action, as Allah Almighty says: "And every soul earns not [anything] except for itself, and no bearer of burdens will bear the burden of another" (Quran 6:164). And as the Prophet, peace and blessings be upon him, said: "No perpetrator commits a crime but against himself; a father does not commit a crime against his child, nor does a child commit a crime against his father." So, be at ease, and supplicate for her well-being.