In one of social network the name of my teacher was written using Mrs + first name. She is 30 year old. I know that Mrs was most often used by a woman when married, in conjunction with her husband's first and last names. So does it mean that she is divorced, or ... ?
Mrs. [husbands_first_name] [husbands_lastname] would be a formal but not quite obsolete usage; could also be considered sexist nowadays. You might see this in places like newspaper wedding announcements or obituaries, or Jane Austen novels.
Mrs. [her_first_name] would probably mean that the person in question is currently married, and would be quite informal and a bit odd outside of an elementary school teacher as Tim says, or a childrens entertainer. :-)
Miss or Ms. [her_first_name] is slightly uncommon and possibly regional, again per Tim's comment, but most native speakers would not find this too odd, and would interpret it as meaning that the subject has never married, for "Miss", or is either older or divorced in the case of "Ms.". A good example would be "Miss Ellie" of the 80s soap opera "Dallas". I think that the Beverly Hillbillies also called Mr. Drysdale's assistant "Miss Jane", while he referred to her as "Miss Hathaway", which supports the idea of this being a regional usage.
[Mrs/Miss/Ms] [her_lastname] would be most common and appropriate; [Mrs/Miss/Ms] [her_firstname] [her lastname] would also be fine, and is what would probably be used in legal documents, for instance.
As the other answers say, any use of the title "Mrs." suggests that the woman is married or widowed (or possibly divorced). If she is using "Mrs." + (her first name) as her "screen name" (user name) on a social media site, that could simply mean that she is doing it for anonymity purposes. Specifically, if people find her profile (i.e., her photograph, etc.) on the social media site, she might want them not to be able to learn her last name from the site (because that would make it much easier for them to find out other information about her, such as her home address).
Nowadays, a Mrs Jones could be the wife of Mr Jones, or his widow, or a woman who chooses to continue using the Jones surname, which she chose to take on as her own at marriage, even after their divorce, because it may be the name she is known by where her children go to school, or for some other personal reason.