Hello!
I am Ukrainian and my husband is British
We got married in August 2016, applied for visa on 25th January 2017 (yeah, took a long time), and we've been put on hold due to court case (read here
immigration-for-family-members/uk-spous ... 26494.html)
It's way faster to marry in Ukraine. You need to come to Ukraine, translate your passport and get notary approval (just go to any translation office). Then you go to ZAKS (registration office). We got married in Kiev, in ZAKS on Pechersk (your fiancee should know; website -
http://zags.kiev.ua/pecherskij). It's really fast there. They proceed your application within 1 month and you can get married. Total cost of this around £10-20.
If you want to get married faster, I've heard about document-service in Kiev "Gotovo"
https://gotovo.net.ua/ , they can register you within 24 hours, but charge around £150 (and I'm not sure is it applicable for foreigners).
Anyway your fiancee should contact those places and find out ("Gotovo" is very friendly and they will provide you with any information).
If she isn't from Kiev, so ZAKS (government registration office might be a problem, as they are not used to foreigners).