If you met her online only and you need to buy her a ticket to visit you - you have your answer already: it is a scam. Check the email address she is using, check her pictures to see if they are not already reported online. If you have no hits, check the content of the emails you received from her - if you find the exact same emails posted anywhere else as a part of a scam you will know for sure how real she is.
If you don't know how to check, use please, my email address - you can find it under every post I made on this site - and forward to me some of the emails and pictures you received. At this stage, for me, it is beyond any doubt you are dealing with a scammer, but maybe you need some additional elements to believe the same.
Anyone you meet online only asking for money - no matter what reason - is a scam.
Help yourself by helping others - report your scammer here.Google can be your best friend
;use it if you have doubts about someone met online. If someone met online only asks for money, no matter what reason, it´s 100% scam.