I want to translate:

> "I gave my little sister a doll for her birthday".

I do not want to use `私` but imply that I did it, so the right particles are
crucial.

I've come this far, but I'm not sure about the particle `は` which I chose
basically because it was the most likely one that was left.

> 誕生日{たんじょうび}は妹{いもうと}に人形{にんぎょう}をあげました.

My original choice was `誕生日に` but then I would have two `に`s.

How can I say "for occasion"?
CC BY-SA 3.0
2015-03-26T20:36:33.120
23473
2015-03-27T00:39:43.090
2015-03-27T00:08:54.140
3035
7355
question
grammar translation particles
Which particle to use to say, "for (occasion)"?
There is no problem having two に particles in one sentence. Your original
choice is most correct.

Using [event]+に is the best way to express that something will happen for
[event], and [person]+にあげる happens to also be the best way to express that you
are giving something to [person].

> 誕生日｛たんじょうび｝に妹｛いもうと｝に人形｛にんぎょう｝をあげました。
CC BY-SA 3.0
2015-03-26T20:50:26.903
23474
2015-03-26T20:50:26.903
3035
23473
answer
As @Eric mentioned, に is the correct choice, and there is no harm in having
two of them in this sentence. In addition to that, you could use には to
emphasize that it was specifically for her birthday instead of some other
occasion.

> 誕生日 **には** 妹に人形をあげました。 → For her **birthday** , I gave my little sister a
> doll.

Note that you can also use [贈]{おく}る for giving a present.
CC BY-SA 3.0
2015-03-26T20:56:40.750
23475
2015-03-26T20:56:40.750
78
23473
answer
To say 「誕生日に」＞「誕生日は」 in OP's context is very Japanese-as-a-foreign-language-
esque.

There is absolutely nothing wrong or unnatural in saying 「誕生日は」. In fact, 「は」
would be a **_very_** natural choice among native speakers.

To attach 「は」, the word does not have to be the grammatical subject of the
sentence.
CC BY-SA 3.0
2015-03-26T23:20:53.897
23478
2015-03-26T23:20:53.897
23473
answer
This isn't literal but it seems natural:

妹の誕生日に人形をあげました。
CC BY-SA 3.0
2015-03-27T00:39:43.090
23482
2015-03-27T00:39:43.090
6823
23473
answer