Might as well add my own 2 cents seeing as I've never posted on this particular thread -
Ahem....I don't believe the egg (nor the facehuggers, or indeed the Ripley & Co. that were seen in ALIEN 3 either) was ever actually on the good ship Sulaco in the first place, due to the fact that I choose to look on the whole of ALIEN 3 as merely being a fevered 'cryo-sleep nightmare' which Ripley had on her safe journey home.
And then she had another in the shape of ALIEN RESURRECTION not too long after that....