Why does the Pasuk give precedence to 'ben Yonah', whereas everywhere else, the Torah gives precedence to 'Tor'?
Ba'al ha'Turim: All others who bring birds bring two, but a Yoledes brings only one. The Torah advises her to bring a young dove, since a Tor remains eternally loyal to its spouse, and, if she were to take a Tor, she would leave its partner in mourning for its entire life. 1
Ha'Emek Davar: Torim are more beautiful. Here, for Chatas, her Korban should not be Mehudar, therefore a Yonah is preferred. 2
Perhaps the Torah advises so only here, for all others bring two birds, and we assume that one who brings two Torim will bring a Tor and its mate! (PF)
Why does it say "Shenaso"?
Moshav Zekenim, citing Nidah 47b: The lamb must be in its first year (we count from its birthday), and not according to years of the world 1 (from Tishrei).
Moshav Zekenim citing Ri: According to R. Meir, who holds that one day in a year is considered a year, no verse is needed! We cannot count according to years of the world, for then no lamb is Kosher for [the Tamid or Musafim of] Rosh Hashanah, since a Korban must be at least eight days old, so it begins it second year on Rosh Hashanah! (Even if you will say that only a full day counts like a year, no lamb would be Kosher for the Tamid in the six days after Rosh Hashanah. - PF)