A. Did your aunt have to travel from out of town to your child's birthday party? It's hard to tell what the situation is since various people know each other. However, if she was making a lengthy trip on her own, I can imagine wanting to bring someone to make it more pleasant. Regardless, talk to her about how that makes you feel... don't just fuss at her for doing it. Ask if she can invite someone else next time, just so you can focus on your daughter instead of the adult drama. I mean seriously, does it matter that she brought someone or that she chose poorly? Sounds like you guys need to spend some time talking honestly to each other. Why did she feel like she had to bring THAT friend? Why would your request for her to choose differently cause her to consider not coming at all? What is she thinking/feeling?
B. Your aunt is prenant. No one is in their right mind when they're pregnant. I totally agree, things are difficult for your relationship right now, but in the end, don't you want to be there for her and be one of those people who stood by her even when she wasn't at her best? You had a child. Do you truly believe you were at your best during all the hormone rushes. I know I had moments where I felt like I was going crazy!
C. You are seriously upset because she picked someone over you to be her coach? No way I'd pick you either... you're from OUT OF TOWN! She could go into labor at 3am 4 weeks early with complications. Are you really expecting her to put all her faith and comfort in knowing you can be there at that time with no prior planning? You said you have to fly. Have you really thought about this? You are not an option... so that tells me you are jealous of their relationship. I'm sure it's hard knowing that you used to be super close and now she's relying on someone else to do things that you want to do. But let's be realistic. You are not an option. You don't live locally.
D. I get the point about the Christmas presents. But do you really want to create a ritual of gift giving with your aunt or do you want to focus on spending quality time? Some people feel like they need to give gifts in order to show their love. Some people know that the true gift is the relationship. Don't get caught up in the materialistic part of Christmas. Enjoy the fact that your relationship rises above that.
If you really want to exchange gifts, tell your aunt that you know you don't normally do this but you'd like to start. Your aunt may only exchange gifts with her friends because they instigated it and she feels like she needs to reciprocate. My mother-in-law does this and every year she wishes her friends would save the money and just have her over for a visit or maybe for dinner. However, she reciprocates the gift because she feel's obligated in order to show them that their relationship means a lot to her too.
All in all, it sounds like you and your aunt are close but not verbally intimate. You guys need to just have a soul bearing moment where you can clear the air and get back to being close and not worry with all the "stuff" that you're caught up in now. Focus on what's important... each other! And don't try to compare yourself to her friends. She is your "sister", and you are not only friends, you are family. That is so much more powerful, but it still needs to be nurtured.
Good luck to you. I hope you guys are able to get it all worked out and be closer for it in the end.
p.s. I completely forgot the main reason you posted... the shower! I would definitely do the shower, but enlist the help of her friends. Give them tasks or ask them to compile lists of ideas from their baby shower expeirences and those of their friends or Google. Divide up the work and the expense. Have it at one of their houses so you don't have to spend extra money and tell them why. Paying for a location and expensive food is a waste. People really just want to enjoy each other.
Find out about decent catering in your area if you need to or consider ordering platters from a local restaurant she likes or from a wholesaler (Costco, Sams, etc). Do fun things that are cheap like babyfood taste tests (buy a few jars, remove labels and mark with a letter. Give everyone pretzel sticks and let them dip and taste. GIve them a piece of paper to write down all their answers and see who got the most) or nursery rhyme identification (gather 10-15 nursery rhymes and then give clues about the rhyme's story and see if they can guess the rhyme). You can do the rhymes since paper travels well, one of them can do the baby food because you can't bring it on the plane. There are so many other ideas you can find online if you don't like these.
Keep the cost down but let the friends be involved. They may really appreciate it, or not. Check back with them a few times to see how things are going and to make sure you have all the bases covered. That way they don't drop the ball and you feel like the effort and cost is distributed. You may do a lot more work since you're coordinating, but your aunt will appreciate the joint effort... if not right away, as she looks back and realizes how many people put the efforts into her special day. And resist telling tales on her friends and how much they didn't do. Let her just enjoy the event and remember it positively. It isn't about everyone being equal, it's about her and that wonderful baby!