וְאִם־לֹ֨א תִמְצָ֣א יָדָהּ֮ דֵּ֣י שֶׂה֒ וְלָקְחָ֣ה שְׁתֵּֽי־תֹרִ֗ים א֤וֹ שְׁנֵי֙ בְּנֵ֣י יוֹנָ֔ה אֶחָ֥ד לְעֹלָ֖ה וְאֶחָ֣ד לְחַטָּ֑את וְכִפֶּ֥ר עָלֶ֛יהָ הַכֹּהֵ֖ן וְטָהֵֽרָה׃ (פ)
И если ее средств недостаточно для ягненка, то она возьмет двух горлиц или двух молодых голубей: одного для всесожжения, а другого для жертвы за грех; и очистит ее священник, и она будет чистой.
Rashi
אחד לעלה ואחד לחטאת THE ONE FOR A BURNT-OFFERING AND THE OTHER FOR A SIN-OFFERING — Scripture puts it (the עולה) first only by way of mention, but so far as offering it is concerned the sin-offering precedes the burnt-offering; thus do we learn in the Treatise Zevachim 90a, in the chapter commencing כל התדיר .
Ibn Ezra
If she cannot afford a lamb [literally: if a lamb cannot be found in her hand] A similar figure of speech is “he cannot afford” [literally: his hand cannot reach] [14:21].
Sforno
וכפר עליה, for during all the days that she had been excreting blood her thoughts had been preoccupied with the phenomenon of semen, etc, and she had therefore not been in a fit state of mind to enter the precincts of the Temple and offer sacred matters.