9-10 months is the usual so that they are over 12mths at farrowing. bear in mind most people will want weaners in april, and after aug, they are alot harder to sell as people want them finished by xmas and away from the farm before winter/mud strikes.
unless you have an established market for meat - i wouldnt plan on winter litters as they are so hard to shift and you may be left with alot of mouths to feed.
id try getting her in-pig asap if i was you and you'll capture the weaner market for june if you are lucky (if she takes first time). by the time you notice and start recording her seasons in time for organising a boar/ai, shel be 10 mths anyway.