Hen do upset

All my adult life theres been a part of me that has dreaded my hen do and wedding day due to having one of those awkward families where there is a lot of politics that could get in the way and make things difficult. In the last few years since having my 1st born she has managed to bring a lot of the family together which is wonderful but there has still been the seed of doubt in my mind about what my big day would look like. My friends have started to arrange my hen do and we have decided to go away to york to go to the races and have an overnight stay. Before setting up a group chat i checked with my most important friends and family to make sure they were up for it and could make the date and they all gave the thumbs up. Less than a week later and my friends have told me that my cousin has said she probably wont make it because she has 5 children and will struggle with childcare. Off the back of this her mum has said she will no longer make it either. If it was anyone else i wouldnt be so upset but having no siblings my cousin has been like a sister to me and over the years i have bent over backwards to attend things for her. I single handily arranged her hen do and spent a fortune on it and also travelled 5 hours away for her wedding in Scotland for 2 nights. Shes had 5 baby showers and I've been to all of them, but when i had my baby shower she said she could only come for an hour and couldn't eat with us because she had 'accidently' double booked me. I found out the other thing she had arranged was a meal with an auntie she had only recently started speaking to again after 10 years of no contact due to a family fued. A meal with family members who had been awful to her in the past and i was there to console her. So that really stung as well at the time. I really feel like ive been mugged off and this is the final straw and our friendship has probably run its course now. I recently told her that id decided to not have children at my wedding so a part of me wonders if shes annoyed about my decision and that's why she's not making an effort. Am i being unreasonable? I appreciate its difficult with 5 children but its a one off and its not like im just a friend. Ive also given her 6 months notice before the hen do so that she can make plans. What makes it worse is that she hasnt even got in touch with me to tell me she probably wont make it and ive had to hear it from someone else. Id probably understand more if she text to explain it was difficult and that maybe we can do something special just the two of us closer to home?