How long does a passport have to be valid for FLR?

[Blitheringking]

Hi people,

My wife will be applying for FLR in a couple of months.
Her initial visa expires on 30/09/2017
her passport expires on 08/01/2019.

Can she apply for FLR on this passport as the passport will expire before the end of the FLR?

I realise it may be a stupid question to some, but I genuinely don't know.

Many thanks.

[CR001]

Passport must be valid at time of appication. Visa will be a BRP card and not a vignette in her passport.