Bridesmaid issues

Hey everyone, I’m having a really tough time. I have chosen my bridesmaids and they have all agreed which is amazing, two of them live abroad and have said they are happy to travel for the wedding. However, one of them is being really difficult, firstly she assumed she would be bringing a plus one as she is a bridesmaid (she is single) and I kindly explained that our wedding is intimate with a maximum of 50 people, and she was a bit pissy with me about that. But now she’s pressuring us for a date and my partner and I are still yet to confirm the exact date with our venue. I explained we need to double check the venue and dates with our parents (my fiancés parents live the other side of the world) before we confirm and that we will confirm asap with our guests regarding the date. She’s now said “I want to be there but be a little bit more considerate for a wedding guest travelling 12,500km”. We have over 10 people travelling this distance, some even further and they haven’t been difficult and understand. I really don’t know what to do, she’s put a real dampener on the planning and it’s affecting my fiancé and I, and I now regret asking her to be a bridesmaid as I’m worried she’s going to continue to be difficult. I’m wondering if anyone has had a similar issue or has some advice.