She would want to get a tourist visa... and she should not mention in the application or to immigration agents anything about getting married. It would complicate things. Her bf or her bf's family should write a letter inviting her to visit with them for some sort of gathering maybe, and she can include this letter in her application, and state the purpose of the visit as visiting friends for a short holiday.
If the flight will be paid for by someone else, mention this upfront in the application, and make sure that she can demonstrate in the application - maybe a photocopy of her bank book - that she has enough money to bring with her. When my bf (now husband) wanted to come here to get married, his first application for a tourist visa was turned down, and they said it was because he didn't seem like he had enough money (he demonstrated that he had a regular job, had about 4000$ in his account, and said he'd be bringing about 500$ in cash, and somehow they thought this wasn't enough for a 5-day visit with friends and family).
Worth a try? Apply for the tourist visa well ahead of the wedding, just in case they reject the first one!