I don't post a lot, so I apologize for the lack of acronyms
Background: My ex-husband and I had my daughter during our senior year of college. We got engaged soon after graduation, married shortly there after and were divorced within a year. We 50/50 parented while we lived in the same town, but he moved on to a better job opportunity in the Big City. I had moved in with my now-husband, and he had moved in with his now-wife. He has her for school breaks and alternating holidays. We're poster-parents for communication when it comes to our daughter, and the step-parents (my husband and his wife) are wonderful additions to her life.
Since he moved away, my husband and I had our son, (now 20mo). My daughter was thrilled and has been an amazing big sister. Now, her dad and her step-mom are expecting, and I'm curious what to expect now that she'll be the part-time kid in a household where there will be a full-time baby. My daughter seems excited - telling her friends and teachers, but I'm worried about the impact it'll have with her already limited relationship with her father. I don't want her to get hurt.
I'm looking for adivce on how to talk about it with her, how to look for signs of uncomfortableness, and interested to see if anyone else has been through the long-distant parenting/half-sibling circumstances described above.