Marriage Visitor Visa Question

Hi there, sorry if this is the wrong place to post this but I have a question regarding the Marriage Visitor Visa.

I am a UK citizen, and my fiance is a US citizen. Due to some problems with income this year, we have decided to use the Surinder Singh route to move here to the UK (but that's another issue entirely). The basic idea is that she would come here, we'd get married, then move to Ireland.

What I'm wondering is does she need a marriage visitor visa, or is that for use when two non-EEA people wish to get married in the UK then leave?

If so, some of the criteria for the visa in question bug me. It says we'd need to show that we've paid for some of the costs up front, and proove that we've given notice to the register office... neither of these things have occurred yet. We're going for something small, just close family and a couple of friends, performed by a family friend who is a vicar. We haven't set a date yet because we're waiting for the visa... and we can't give notice unless she's here in person... so it seems like we're in a Catch 22 situation?

The short version of this is; does my US fiance need a marriage visitor visa to visit the UK and get married to me, a UK citizen, or would she be able to come in under her normal visa waiver. Either way we're moving to Ireland once we're married, and we haven't currently made concrete plans due to, if this visa is a no go, we'll get married in the USA.