Best to be certain as to your wife's immigration status.
Check the documentation.

Based solely on what you've shared it seems that your wife arrived to UK on a fiancée visa which was applied for after 9 July 2012 with subsequent FLR(M) application.
Means she is on a 5 year immigration journey and is now looking to make application for her second FLR(M) period of 30 Months.

There's a significant amount of documentation to prepare.
You should also carefully review her English Language status as the rules have changed a few times and it's likely she'll need to update that

Here's the form:-
https://www.gov.uk/government/upload...R_M__11-15.pdf