First of all, +1 on this wonderful question, which has been causing great contention between man and wife for generations upon generations.
Fortunately, this is a case for which we can wholeheartedly say "לא אלמן ישראל", for two reasons:
The sages who set down our daily prayers knew that this instruction might become vague as the generations' moral sense decreases, so they explained this instruction by immediately following it with other verses (as shown below).
We're talking about cases where "לא אלמן ישראל", i.e. this question is relevant in cases where there are both a husband and a wife present.
Firstly, notice that in many cases, we interpret the text's meaning based on the tradition of the cantillation. Example:
This Mishnah Berurah OC 51, 17 states that in Shirat HaYam, one should pause between "במים" and "אדירים", and that the word "אדירים" describes the Egyptians, not the water. This is based on the cantillation: צָֽלְלוּ֙ כַּֽעוֹפֶ֔רֶת בְּמַ֖יִם
אַדִּירִֽים. Notice that the Tifcha signals a slight pause, which proves the Mishnah Berurah's opinion.
A different example (some say from the Vilna Gaon) where we can see that the cantialltion has wisdom and clues behind it, is in Esther 2, 14: וּבְהַגִּ֡יעַ תֹּר֩ נַעֲרָ֨ה וְנַעֲרָ֜ה לָב֣וֹא ׀ אֶל־הַמֶּ֣לֶךְ אֲחַשְׁוֵר֗וֹשׁ...
When the women were called to the king, they came willingly, as the meaning of the cantillation Kadma Ve'Azla ("came early and advanced") hints. However, when it was Esther's turn:
וּבְהַגִּ֣יעַ תֹּר־אֶסְתֵּ֣ר בַּת־אֲבִיחַ֣יִל דֹּ֣ד מׇרְדֳּכַ֡י. We see four consecutive Munachs, which hint at her unwillingness to go (Munach comes from "נחת", resting, walking slowly).
There are many other enlightening examples, but let's see now what the cantillation say in our case:
וַעֲצַ֥ת יְ֝הֹוָ֗ה הִ֣יא תָקֽוּם
There's a slight pause of the Munach on "היא", which hints at two things:
- The Munach is under "היא", which means she should rest (Munach is from the root of resting).
- Since there's a pause by the Munach, we must read "היא - תקום" - that the man must get up.
Secondly, let us now open our morning prayer book and see what are the next verses in line (before Ashrey):
רַבּוֹת מַחֲשָׁבוֹת בְּלֶב אִישׁ, וַעֲצַת ה' הִיא תָקוּם
עֲצַת ה' לְעוֹלָם תַּעֲמֹד, מַחְשְׁבוֹת לִבּוֹ לְדֹר וָדֹר
כִּי הוּא אָמַר וַיֶּהִי, הוּא צִוָּה וַיַּעֲמֹד
We can see that they left us no room for doubt. The second verse says "עצת ה' לעולם תעמוד". But still, does "תעמוד" mean the husband should get up (גוף שני), or the woman should (גוף שלישי).
So "בא הכתוב השלישי ומכריע ביניהן", we have the third verse to remove all doubt and solve our problem: "הוא צוה - ויעמוד"! Finally, an explicit command that the husband must get up.
Also note that these problems and tribulations were hinted in this last verse, in a more explicit way than mentioned:
"כי הוא אמר ויהי": When we reach the situation of "ויהי" - Chazal teach us in Megillah 10b:
אמר רבי לוי ואיתימא רבי יונתן דבר זה מסורת בידינו מאנשי כנסת הגדולה כל מקום שנאמר ויהי אינו אלא לשון צער
Said Rabbi Levi, or some say Rabbi Yonatan: We have a tradition from Anshei HaKnesset HaGedolah - anywhere it says "ויהי" - it is a sign of sorrow.
Some explain that "וי" and "הי" are both roots of trouble and weeping ("הי" is the base of "נהי").
So we see that "כי הוא אמר ויהי" - when we have troubles (between the parents) and weeping (of the baby) - "הוא צוה - ויעמוד" - the man must get up and take care of it. ודו"ק.