Husband’s SIL is acting weird

I had my first sonogram yesterday (10W5D) and we got to see my little love’s heartbeat. I showed close friends and family. I showed my husband’s sister-in-law and she had the worst reaction ever. Didn’t seem excited (which is fine, not her baby) and when we told her the EDD she said “As long as it doesn’t fall on [her husband’s] birthday,” in a completely serious tone. I was so confused? During her pregnancy, we were all so excited for her and shared the excitement together. Her son is now a year and a half and husband and I are his godparents. They were our sponsors for our wedding. We used to be close. I just felt sad.