If she is a legbar cross, I would expect to see a slight crest.... it might be miniscule but I believe it is a dominant trait. I can't make anything out on that photo as it isn't close and light enough to see.
Legbars are more common here in the UK than araucana or EEs, so it is the first breed to think of here when you see an egg with blue shell genetics. Particularly a salmon breasted single combed bird with leghorn type body shape... although legbars should be a bit more substantial than leghorns of course.
It really is a stunning egg both in shape and colour. Many congrats.