http://www.ukba.homeoffice.gov.uk/visas ... you-apply/
What was the start date of her visa and when does her visa expire? In the link above, which is the 'Can You Apply' it says :
You cannot apply in a partner category if you:
are the spouse or partner of a person who is settled in the UK or has British citizenship if their most recent permission to stay was under tiers 1, 2, or 5 of the points-based system; and
you do not qualify for settlement yet.
Instead, you must apply as a dependant under the relevant category of points-based system.
If you made an application to enter the UK on or before 8 July 2012 please see the Partners who applied on or before 8 July 2012 pages.