Name help

Venting, but also looking for suggestions of how to handle this situation. SIL is also pregnant, she’s due a couple months after me. When we found out, my husband was proactive and told her the middle name we plan to use (a combo of their mom and dad’s middle names- there is no other way to combine the names into a cute name). Well, here we are a couple months later, she did her gender reveal and baby name reveal today… and is using the middle name we told her we were going to use. We hadn’t announced the name to the family yet as we are still between 2 first names, but hoped to announce it at my baby shower in a couple weeks. My husband and I are both pretty upset. He immediately tried to talk to her about it today and she said she’s wanted this name since she thought she was pregnant last year (was not pregnant, apparently had a really bad UTI that popped tests positive), but she said nothing about it a few months ago when he said we would be using this middle name. My husband does NOT want to give up the name, he even said he still wants it even if she uses it too, but I want our kid to have her own name.