Hmm.
Don't think it is rude as such, but it very about you...
I mean, I think I probably would have been a bit more enthusiastic about HER day, about HER celebration...of course, that is with hindsight! lol

If it were me, I would send her another text, or call her, and say something like: I am sorry if I was rude in the earlier text, the date made me feel a bit emotional. But I wanted to let you know I hope you enjoy your shower and I am sorry I won't be there for you to help you celebrate your baby! Baby showers really stir some emotions in me and I don't feel comfortable bringing that dark cloud to your happy day. Can't wait to see the photos on FB, and again, I am sorry if I was a bit rude earlier. xox

I am sure if she is a good friend she understands though and perhaps just couldn't reply at the time.