Heartbroken!! long post sorry!

I am expecting my first baby 16weeks on Monday. I am the oldest girl out of my family so I thought my mother would be thrilled and do anything to be here with me!  (My husband and I are currently stationed in Japan) In the beginning when we first told her she was excited and was planning on coming for the baby's birth. We planned on paying for her trip and everything. Then out of nowhere she tells me my dad told her she couldn't come! So me being  devastated called my dad and asked why! But he says she hasn't said one thing to him about coming and he wouldn't care if she came! So I tried to just forget about it and tell myself I didn't need her here I could do it on my own. She still has no idea I asked him and stands by her lies! Then my sister in law announced! ( I am beyond excited for her and I to be expecting at the same time) she's Due the day after me with her 3rd baby! I'm heartbroken because my mother is choosing her over me! (This is not the first time my mother has done something like this)  I feel like this was my breaking point with my mother! I don't even know what to think anymore she has hurt me so much!! How do I deal with this?