I suppose it depends on how badly it broke. If it's just a single piece it should be relatively easy to glue back on using a glue that dries transparent. Most super glues would work. You didn't say if it was a painted or decorated egg, I'm assuming it's just a regular Ostrich egg. If it is a regular egg and the sentimental value isn't important, it can be easily replaced. You can use the search box on this site by typing in eggs and finding a rancher that probably sells empty eggs.