No, she MUST hold ILR before she can apply for citizenship, but she does NOT have to hold it for 12 months.
There are slightly different residency requirements for citizenship, depending on whether you are married to a UK citizen at the time of applying or not.
For those married to a UK citizen, the residency requirements are:
- must hold ILR (for any length of time)
- must have been physically present in the UK exactly 3 years prior to the citizenship application date
- must not have been outside the UK for more than 270 days in the last 3 years, with no more than 90 of those days in the last 12 months (you don't count the day you left or returned on each trip)
However, because it takes 5 years to qualify for ILR, you still have to wait 5 years until you have it before you can apply for citizenship. It used to only take 2 years to qualify for ILR on a spousal visa, so the 3-year citizenship requirement made more sense.
For those NOT married to a UK citizen, the residency requirements are:
- must have held ILR for at least 12 months
- must have been physically present in the UK exactly 5 years prior to the citizenship application date
- must not have been outside the UK for more than 450 days in the last 5 years, with no more than 90 of those days in the last 12 months (you don't count the day you left or returned on each trip)