Wow. Six months? Was there a medical reason for this other than giving birth? We only waited until the post-partem bleeding stopped.
If she had a vaginal birth, you might notice a couple of differences, most notably being she might not be as 'tight' as she used to be. This will vary but don't be alarmed if that's the case. She may also have developed hemmorhoids-again, nothing to really be concerned about unless they're severe and active.
If she had a ceasarian, nothing really changes at all internally(a boon to that procedure!)
Is she nursing? Nursing increases oxytocin, which has a few uses, one of which is increased horniness.
Otherwise after six months she should be as close to normal as she can be. Take it slow, enjoy the 'reentry', making sure to show her she's still the same desirable woman she was before. And make sure the baby has been fed really well, changed and down for the night! Nothing kills the mood faster than 'WAAAAAAAAAAAAAAHHHH'
