It is sometimes hard to let go of control once you have it. And real life (tm) can get in the way. I think it is sometimes useful to be able to state an exact place and time when things will happen that you both stick to no matter what. i.e. make arrangements so that one night every week she is yours completely, no matter what (as in only a serious emergency will break this). You make sure that the kids are looked after (babysitting, sent to the pictures or to visit friends, whatever works for your family), there is nothing else planned and so on.

Another thing you could try is to use communication with her at work to impose your control over her in more normal cirumstances. You have to be careful not to compromise her at work, obviously, but there are things you can do to make her feel owned and wanted. For example, send her a text message or e-mail (to her nonwork account) describing things you want to do to her or describing a task you want her to do when she gets home.