Its highly likely that Soubry is on leave, as is the vast majority of the Govt and the Armed Forces. Her reply is likely being co-ordinated ahead of a return to work tomorrow when she can get more information.
She is, by all accounts, an excellent minister and one that everyone I know who has dealt with her has rated very highly as being passionate and in charge of her brief.
I wouldn't let a story breaking in the main leave season during a quiet time of year when many are away cloud judgement. The other point to note is that it would not necessarily have hit a Ministers desk to dispose of this site or others - without wishing to sound harsh, as this is a fairly routine process of disposal of a site no longer used by Defence, I'd argue wouldn't have needed to go to be briefed to a Minister who, IIRC doesn't lead on disposal of defence estate?