Well, they noticed the bite marks immediately and that caused quite a bit of stir. In any case, there should have been a doctor, nurse, orderly, somebody watching her. For her to be all alone (so much so that no one was in the area to notice the screaming) was pushing it a bit too far.
Well, I don't think there's anything in the movie to hint that the virus had undergone some kind of mutation, but in any case if that were true then everybody that the father infected would have the same strain of the virus. The rest of them didn't seem to be anything but your regular angry as ****, not much in the way of subtlety, rage victims.
I'm sure they could have asked their dad, given his position he could have pulled a few strings to get somebody to drop by the house.
Actually, the outbreak into Europe occurs because of the Army's indiscriminate killing following the fire bombing, not in spite of it.
If the Army had tried to rescue survivors, and they could clearly be differentiated from the Infected, then they would have been able to control the movements of the survivors, put them into quarantine and run tests to make sure everybody is clean.
And honestly, that's what the army WOULD have done in such a situation.