There are a few factors that can make a difference.
First, what does her passport look like? has she travelled anywhere?
IE: Europe, US, Etc before? If not it lowers her odds.
Some of the other factors will be, connections to home ( she must be able to prove these) Money to support this trip, etc. How long have you known each other?
How many trips have you made to meet her, family and or friends.
Do you have any proof of this?
I will explain my storey briefly, keep in mind it was with women from Ukraine.
I have done this twice, once with girl I met and with my wife now.
I had been there too visit and on second visit, I had all documents prepared.
We went to Canadian embassy and dropped of documents together.
I did do invitation letter.
I kept it simple and to the point, with information and facts.
I did not buy plane tickets in advance, I gave approximate travel dates,
that I would provide return ticket, proper travel insurance, place to stay and all
required for the visit. Along with some personal facts of our relationship.
First time, they sent 6 month travel visa, no questions asked.
2nd time, the sent an email, requesting some photos, I managed to call and speak to someone. Said listen, I am in _________ Apartment now, Pictures are home in Canada, can send when I get back, but if you would like we can both come in and meet you, as we are only an hour away. 3 days later we had visa. Did not need to go to embassy.
This is how I did it and it worked, simple, honest and straight forward.
This does not mean it will work for you. Check as much info as you can, make sure
all is done correct and decide how you will proceed.