Does what they did online—lustful talk and actions resembling fornication—count as fornication?

What you did with this woman is considered a means to zina (unlawful sexual intercourse), and Islamic law has called it zina because it is a means to it, as stated in the noble Hadith. You have done well by repenting to Allah, and it is incumbent upon you to be cautious in the future about anything that might lead you to such acts, like unlawful seclusion (khalwah). You must follow the path of the righteous.