There is no reservation in Islam against women participating in online discussion forums as long as participating men and women adhere to the Islamic manners and proper etiquette.
Dr. Sano Koutoub Moustapha, Professor of Jurisprudence and Its Principles at the International Islamic University, Malaysia, states the following: First of all, I would like to stress that Islam does not prevent a woman to talk to non-maharms unless talking is leading to an evil end.

It is allowed for a Muslim woman to take part in any useful and meaningful discussion as far as the discussion doesn’t contain any violation of Islamic teachings and morality. Therefore, the objective of talking and communicating will determine the lawfulness and unlawfulness of the action.

Looking at the history of Islam, one finds that Muslim women used to talk and communicate with non-mahrams within the Islamic teachings. I have never come across any statement from the Glorious Qur’an or the Prophetic Hadith prohibiting a woman from talking to a non-mahram.
Furthermore, the Qur’an did advise how a woman should talk to a non-mahram in Almighty Allah’s saying, (O ye wives of the Prophet! Ye are not like any other women. If ye keep your duty (to Allah), then be not soft of speech, lest he in whose heart is a disease aspire (to you), but utter customary speech.) (Al-Ahzab 33: 32)
Based on the above, Muslim scholars are of the opinion that a woman is allowed to communicate with non-mahrams as long as she abides by the Islamic manners and there is apparent necessity for such discussions and talks.