Is she right?

I'm a bridesmaid for my best friend later this year. By the time her wedding comes I'll be about 30 weeks pregnant. My husband and I have struggled to have a family as I have some gyne issues so this pregnancy is a total shock and massive blessing. I told her very early on, offered to buy a new bridesmaid dress, or stand down as a bridesmaid. Neither of which she took me up on. She did say though that's it's an 'unwritten rule that you're not meant to get pregnant when you're someone's bridesmaid'. She says she's happy for us but is taking very little interest in my pregnancy while I still do all MoH duties and try to get excited about her wedding. When she was my bridesmaid I'd have been delighted for her to be having a baby, it's a blessing that can't be timed!! My husband is furious at her for saying that. I just feel confused and don't know whose in the wrong! She's been engaged for years. Is she right about it being an unwritten rule not to get pregnant???