The Talmud (Ketubot 61a) states that a woman can perform any service for her husband except for three things, one of which is mezigat hakos:
אמר רב יצחק בר חנניא אמר רב הונא: כל מלאכות שהאשה עושה לבעלה - נדה עושה לבעלה, חוץ ממזיגת הכוס, והצעת המטה, והרחצת פניו ידיו ורגליו
Rashba writes (Ketubot 61 and elsewhere) that this refers specifically to wine:
פי' של יין שהוא סימן לחבה
The Shakh, (YD 195:13), however, indicates based on the Tanna D'Bei Eliyahu and Sefer HaTerumah that she should be stringent not to present him with even other drinks, and even foods [i]:
אבל להביא קערה המיוחדת לבעלה אסורה וכדמוכח מתנא דבי אליהו וממ"ש סה"ת דאף בהושטה בלבד כשאין בו שינוי אסור במאכל ובמשתה ע"כ ולפי זה משמע דמחמיר ג"כ בשאר משקים
The Arokh HaShulhan (YD 195:13) states that passing food to him is fine:
אבל להושיט את המאכל וכ"ש לתקן המאכל מותרת
The Yereim (26) writes that the prohibition is only where after the meziga she passes it to him.
פי' מזיגת הכוס ומושטת לו אבל מזיגה בלא הושטה שרייא
Similarly, the Shulhan Arukh (YD 195:10) states that she may not do mezigat hakos and then place it in front of him. (Note that he does not say 'pass it', but 'place it in front of him'):
שֶׁאֲסוּרָה לִמְזֹג הַכּוֹס , וּלְהַנִּיחוֹ לְפָנָיו עַל הַשֻּׁלְחָן
Ritva in Ketubot (there) quotes an opinion that the prohibition is only where she adds water to the wine and then gives it to him, but giving it to him without diluting would be okay, but he rejects that view.
[i] However it should be noted that this is not the best presentation of the Sefer HaTerumah. The Sefer HaTerumah (82) is actually discussing the custom of some for husbands and wives not to pass anything back and forth when she is a nidda. The Sefer HaTerumah notes that Ri demonstrated that that certainly is not the halakha. According to the halakha, only wine is forbidden. Then he mentions the Midrash Tanna D'Bei Eliyahu quoted by some as a proof that nothing may be passed and concludes that even the Midrash isn't proof, as it might only be referring to food items. However, he never says that he is disagreeing with his mentor Ri, and asserting that the halakha is that any foods may not be passed. Indeed, he concludes that avoiding passing things in general is a good custom and makes no distinctions. Lastly, he is talking about passing, whereas Shakh extends this to presenting him with something.