First off, Bethany, there are multiple women-owned business certifications and they all provide different benefits & reach completely different audiences. Without knowing specifically which one you're talking about, it's hard to provide as thorough of advice, but I'll do my best to give an overview. Before I start, though, Richard's advice is HORRIBLE. NEVER pretend to have a certification you don't. EVER. Not only is it misleading, but the WBENC community (one of the certifying entities) is particularly on it and the corporations they serve will stop doing business with you if they find out you branded yourself as a WBE (woman-business enterprise) without going through the certification process.
So, let's go:
1) The federal government offers a certification, as do state and, occasionally, municipalities and counties. These are a complete waste of time and money unless you plan on doing business with the issuing government or a utility in that area. They are not accepted from one area to another (ex, you can't use a Texas certification to apply for WBE-earmarked contracts in Tennessee). Again, unless your client is THAT government, I wouldn't bother.
2) WBENC (Women Business Enterprise National Council) offers a nationally recognized certification that the government does not honor but that corporations do. If you want certification to get in front of Coca-Cola, Marriott, Pfizer, companies like that, this is the one you need. This certification can be HIGHLY effective if your normal sales contact is in procurement, if you're selling something that is typically awarded through RFPs, or if you're selling something that's not innovative. What I mean by that is supplier diversity officers make no purchasing decisions but connect you to their internal buyers and provide you with information about when your good or service comes up for rebid and who the current contractor is. This means they have to already buy it. If it's something they don't know they need yet, a new service that won't have an existing contact to replace, etc. they can give you insight as to how their organization purchases but that's it. As a result, the women who benefit most from this run manufacturing or logistics companies. Service businesses have a harder time and if you're in tech, forget about it.
3) WEConnect International. Exactly what it sounds like: An international certification. As they partner with WBENC, you do not need this in addition to WBENC if you're selling abroad. Like WBENC, this is also for selling to corporations not governments.
For all certifications the company must have 51% female ownership (for transgendered, they go by what's on your license). In addition, a woman must make all "control" decisions--who to hire, who to fire, a signatory role at the bank, etc. Be prepared to show up to 3 years tax returns (for WBENC, whether companies younger than this are allowed to apply depends on your region), existing contracts, etc.
Also be prepared to "work" the certification--go to WBENC conferences, etc. There are hundreds of thousands of certified companies and just having a piece of paper that says, hey, I'm a woman will do jack sh*t for you. You'll have to enter your profile in hundreds of supplier diversity databases, the vast majority of which are a black hole. Expect a 2-3 year sales cycle on supplier diversity managers making the connection. If you have multiple potential buyers in a company expect them to only introduce you to one and move on to the next lady in line. It's a lot of work for very little return unless you meet all the market factors described above.
Hope this helps.