I need advice on how to deal with my sister!

A little back story, my boyfriend and I started trying to have a baby back in June 2017. We ended up pregnant that November with twins. We lost the pregnancy in February 2018. We lost another pregnancy in June 2018. We are now pregnant with a single baby due June 29th. My sister who always said she was unsure if she wanted kids got married in August 2018. This summer she started trying to conceive. All was well between us, she was working for me and even asking for advice on the subject... until we found out we are expecting. Now she quit working for me, which is fine with me because I don’t take much to heart. But when I told her I heard the heart beat on a Doppler app she didn’t even respond. I went to my first appointment a couple weeks ago and all is well. Our doctor who we have had throughout all of this is very confident that this baby will make it through. I’m heart broken because she doesn’t ask anything about the baby, and I don’t tell her. I don’t know why I should if she doesn’t care. I saw her the other day and she had the audacity to say she can’t get pregnant. I told her “it’s not that you can’t, look at my situation, it took us about 2.5 years to get to this point.” I’m just feeling really hurt that she is being so selfish, and even more hurt that I feel like my sister is obsolete during a period of my life that I always thought she would be here for. I’ve been leaning on my brother a lot but I haven’t opened up to him about how she is acting because I know she is hurting and I do not want to cause any drama. Any advice to help either of us would be appreciated.