I would just get her wipes.
These days I just take the path of least resistance. I really do not care to put 1 second of energy into "making a stand" anymore for stupidity or crazy.
I take a stand if something is genuine and necessary.
I would return the gifts I had already purchased for her, and get my money back.
I would get what she asked for (the wipes and diapers). That's just what I would do. You should do whatever YOU think is best.
OP, I'd be totally irritated too but if, in general, I liked her well enough (even though her behavior had no class) and in the interest of being a team player at work, I'd probably just return what I bought and get her what she asked for.
Much of these work functions are just all about team building and creating a pleasant, supportive work environment that I would just participate with a smile on my face.
However, I'd definitely think less of her and the next time she ever dared to utter a complaint in public, I'd probably be sweetly say "yeah, but it's the thought that counts and it's pretty rude to complain about people's generosity." Of course, you'll probably never get that opportunity.
Your hubby is right, but only because its a co-worker.
Return the nice items you wanted to get her and buy the cheap stuff.
Put smile on your face and attend the train wreck shower.
Make sure to include the receipt of the diapers, just encase.
In this situation, there are all kinds of things I'd
like to do and/or like to say, but, like the above PPs, I'd just return the items I'd already bought & buy a package of Pampers Swaddlers & be done.
Your coworker sounds like an ungrateful, rude, & entitled person, & I can't stand those kinds of people. However, you can't change people - you can only change your actions/reactions. And I'm to the point where I just refuse to let people's rudeness & self-centeredness change who I am as a person.
That's not to say that if she did end up saying something to me about only wanting diapers or complaining about the other gifts she did receive, that I wouldn't say something back to her.
Regarding showers for 2nd babies, it used to be considered bad manners/etiquette in my region (the south), but it's becoming more normal & more of a "case by case" kind of thing.
Personally, I think each baby should be celebrated.
I was a given a church shower & a work shower for our first baby, a girl. Our 2nd child, a boy, was born 18 months later, & I didn't have a shower which was fine. 8 years later, some co-workers insisted on giving me a shower for our 3r baby, a boy. I was worried that people would think a shower for a 3rd baby was in poor taste, but the shower ended up being so lovely. And, of course, since it had been 8 years, we needed baby things again!

They included all of us (my DH & 2 older kids), & it was such a nice time for our family.