If your future spouse can get a B2 visa issued to her, then go for it. But I don't think it's realistic to think she will. She will most likely stumble upon the INA 214(b) "immigrant intent" wall and be denied as "someone who fits the profile.."
Now, if you are a US citizen, you can file for a Fiancee visa to bring her here, but I don't think you are, since if you were, you would have so stated here.
The I-130 petition, then, remains your only option. Marry her and file is ASAP in order to secure the priority date. Then try to become a citizen ASAP as well. You can then bring her much sooner.
Behar Intl. Counsel 619.234.5962 Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
The issue in B1/B2 visa issuance is not disappearing into the population after entering the country, but whether the visa is going to be used for the intended purpose. A person intending to come into the US to immigrate on the basis of marriage is supposed to come in on an immigrant visa, obtained through consular processing of a petition for alien relative (I-130). A person coming in as a visitor actually makes a representation on the forms that he or she is not intending to come in as an immigrant. In the application process for a visitor visa they will want to know the purpose of the trip, that your fiance has a residence and job to return to in Guyana, and that she possesses a round trip ticket; otherwise, they will deny the visa to her particularly if they suspect the real purpose is to marry within the US, which is considered visa abuse.
If someone violates that rule, comes in as a visitor and applies within the US for adjustment of status as the spouse of a U.S. citizen having entered as a visitor, then the entry as a visitor can taint a petition, which can be denied for "pre-conceived" intent of the immigrant at the time of entry, but the USCIS officer can choose in his or her discretion to ignore it and approve the petition anyhow. However, if the person lied in Guyana to obtain the visitor visa and this comes out in the USCIS interview, then the situation is very different, actual fraud may be alleged, and then a waiver may have be to be applied for, which complicates the case enormously.
You should not proceed this way since a lie to obtain a visitor visa could greatly harm future chances for your fiance. Another way to proceed is to marry her and wait with her in Guyana until a consular processed visa is obtained. Please see the links below for explanations of the differences between consular processing and adjustment of status.
This is general information and not legal advice and no attorney client relationship is created.