beyond the pale wrote:

It's been
just over 4 years. I am debating if it's rude to "turn down" a shower, and I
am debating if it's rude to let her throw the shower but have her somehow
let people know that we saved everything and will only need some basics and
mostly diapers and wipes. I don't want to dictate my shower, you know?

It's not rude to turn down an offer to throw a shower. Just
say, "You are so kind to think of me, but I would just be too
embarrassed to put people through that trouble after they'd already
been kind enough to throw a shower for my first. My mother would
have my head on a platter if I accepted your kind offer." Then,
if she continues to press it because she wants to have some sort
of celebration, you can say, "If you really want to do something,
maybe we could just have a little tea or something after the baby's
born so that folks can meet him/her--but please, not a shower where
people feel like they need to bring a gift." Even if you do some
other kind of party, people may still bring gifts, but at least
the gift-giving is not required. What they choose to do is their
own business, so you accept it graciously. If people ask what you
need/want, you can always say that you have everything from the
first time around, so you don't need anything big and really it's
just the consumables that you're saving up for this time.

I
thought maybe it's better etiquette to put up a small registry that she can
enclose on the invitations and if people go look, they'll SEE that it's
small, and contains mostly necessities such as diapers.??

Even with a shower, it's not really proper to enclose
registry information with the invitation.

Or just let her
throw the shower and say nothing at all and maybe people will get things
like that anyway? My husband still works with these people and he doesn't
want to have another shower thrown for us, he doesn't want for anyone to be
able to comment that it's our 2nd shower. Are 2nd baby showers (meaning
showers for Baby #2) tacky in general?

They are not properly done. You can have any other sort of
party to celebrate the arrival of this baby (and guests may well
choose to bring gifts to it), but not properly a shower. People
get all confused because they think that showers are about celebrating
the baby. In fact, they're not. Showers are a party where the
*woman* is "showered" with gifts of small, practical things she
will need as a result of a change in her position (e.g., things
to set up housekeeping as she moves from being single to married,
or things to take care of a baby as she moves from not having
children to having children).
If the goal is to celebrate the baby, you can have a
breakfast, brunch, luncheon, dinner, tea, Christening party,
naming party, welcome home party, pool party, picnic, meet-the-
baby party, or whatever other party you can dream up. Not only
that, but anyone (including the parents) can throw the party,
and they can invite anyone they want and as many or few guests
as they want. None of those parties require folks to bring
gifts, so all you're asking is for them to share your hospitality,
and you can do that anytime you please.

Best wishes,
Ericka