My wife was in Brooklyn today and picked up an advertising magazine that had a short article of he'oros on kashrus and Purim by a Rav who lives inthe 5T-Far Rock area. He mentioned that one must renounce ownership over the funds and food for mishloach manos and matanos l'evyonim given to one's wife, because otherwise the food and money is not hers based on the principle of "mah shekansa isha kanah ba'alah".
B'mchilas kvodo, I do not think this is correct. Such a hakna'ah would be necessary if there was a halacha of "lachem" (like by lulav) which indicated that the mitzva must be performed specifically with one's own funds and food. (Parenthetically, I have yet to see anyone be makneh one's lulav to one's wife on Y"T rishon). There is no such requirement of "lachem" for mishloach manos or matanos l'evyonim.
(See Halichos Baisa ch 24 footnote 55 in the name of R' Shlomo Zalman Auerbach who makes the same point. For those intrigued by the lulav issue for wives, see The Tosefes Bikkurim in the back of the Aruch l'Ner on Sukkah on S"A siman 657)
One other note in passing: according to the Pri Chadash and GR"A mishloach manos is davka "ish" l're'eyhu, to the exclusion of women, who have no obligation.