When I first read the title I thought it was the 3rd shower fo the same baby. I would not attend that! However, I then read the post...
For what it is worth, I'd go to a shower for any
kid regardless of whether they were the first, second, 8th or 10th child in a family - just to celebrate the birth of a new life and make the mother to be feel special for a day.
If a shower is for the first child I give a bigger gift - a baby car seat or whatever - that the family needs, but for all subsequent children I just give a smaller gift - clothes, a toy, a book. If I were invited to a shower for the 10th kid I'd give the mother to be a savings bond cause she'd sure need it when the kid gets to be college age
It's not about the gift - it's a celebration of a new life.
And also, some showers are suprises. Sometimes the mother to be doesn't know that people are throwing her a shower until she arrives. Also, I know someone that had a shower and then had a stillbirth in the 8 1/2 month mark. When that person got pregnant again a year or so later people were very cautious, but they did throw her a smaller shower just to make her feel special. She didnt' keep much from the first shower - too painful- and they didn't want her to always associate the baby shower with sadness. (the second pregnancy resulted in a healthy baby). So you can't always say that the parents to be are greedy or that a shower for anything but the first baby is wrong until you know the entire set of circumstances.
I would talk to your neighbor and if she liked the idea I'd throw her a shower. She doesn't have to register and the gifts don't have to be big. But if she's never had a shower before and this is the first girl it might be nice for her to experience it, and it would make her feel special.