The actual issue here is the mum-to-be has FOMO. She's already left her home city and friends, so has just had a big life change, and now she's pregnant, the biggest life change a woman can have (in my view).
Such big changes in her life, and then to have her best friend's wedding and hen do, I totally get that she has fear of missing out. She's likely feeling a little left out since moving away.
But all that said, these are things she has to come to terms with, and if you really don't want her baby at the hen do, that's your decision, and that's ok. I think she is right not to want to leave her baby, I wouldn't either, therefore, she really needs to accept that she can't have everything she wants sadly.
If you're planning a big night out, baby wouldn't be allowed in the venues anyway, and it's unfair of her to expect you to have a baby-friendly hen do.
I can't remember if you've already offered to go see her in Dublin, but if you haven't I'd absolutely do that, then you can both go do an Afternoon Tea over there or something together, with baby.
I'd broach this very sensitively with her...say something along the lines of:
"Jane, you know how much I love you, and I'm so excited for you having your baby. However, I really don't want a baby-friendly hen do, please do not take offence, but it's a big thing for me and I want everyone to relax and let our hair down. I absolutely understand that baby will be too young for you to leave, that's why I'm absolutely ok with you not being able to make it, I would never expect or pressure you do leave baby.
I really do appreciate your feelings of feeling left out, I understand this is a big life changing time for you. Would it help if we did a couple of fun video calls with you whilst out? Or would you prefer us not to mention it? I really want to work with you to make you feel ok about not being able to join us, so I'm happy to follow your lead with this.
Jane, instead, I'd really love to fly over to Dublin and have an Afternoon Tea with you and baby instead. I'd love to meet baby when he/she's here and spend some quality time together. I'd love to see your new home and see a snippet of our new life over there! I really hope that this is a good compromise for us both. I love you xxx"