Dam betulim

She may attribute the ketem to the borrower only if the borrower is not adversely affected by having the blood attributed to her.

For example, if the borrower is already timeah, either a nida during the seven days after the first time she saw blood, or a zabachtanah on the day she saw blood for the first or second time, or Or alternatively, if the borrower does not become Tmeiah even when she herself bleeds, like a Yoledet during her period of Dam Tohar, or a Betula whose Dam Betulim is still an open wound.

But, if the borrower is a Zavak Tana on her Yom Shimur, or a Zavak Dola during her Shivani Kiyim, then neither woman, lender nor borrower, can attribute the Ketam to the other one, because both are equally affected, for the worse, by having the blood attributed to them.

Therefore, both women are tmeyot due to the ketem.

Ha'rei zom uteret lev'ala ad sh'techia makah, sh'kol dam sh'tireh machmat ha'makah hi, v'im ratah dam achar sh'techia makah, ha'rei zonida.

Dam betulim, as we discussed in Hilchot Ishut regarding ta'anat betulim, is blood which comes from the rupturing of the hymen during a woman's first act of sexual relations.

It is completely tahor, because it doesn't come from the uterus.

Rather, it is considered blood from a wound.

ויהיה דם בתולים זה כאילו הוא תחילת נידה.

ובאוגרת שלא ראת דם ימיה, נותנים לה כל לילה הראשון.

What if she married as a na'arah? For how long can we assume that the blood she sees is dam betulim? If she never had a menstrual period before this, then she may have tashmish for four days and four nights and assume that the blood is dam betulim.

After the fourth day and night, if she is still bleeding, she must be concerned that it may be dam nida.