I'm a mother, not a "birthmother' as i never stopped being a mother and am not an incubator, thanks. Nor am I a "first mother," for the same reason -- my motherhood wasn't taken away from me and given to the next woman in line.
As a natural mother (no, adoption is man-made, not natural), I can answer your question.
Yes, I do resent the woman who adopted my child, for 3 reasons:
Firstly, he ONLY reason why mothers were coerced into surrendering healthy white infants was because of market demand for them -- this shows in how African American mothers were not only encouraged to keep their babies but they were told about resources that would enable them to do so -- no demand from infertile couples for AA babies, you see. Instead, it was white mothers who were herded into maternity prisons ("homes") a.k.a. baby farms. If her and thousands of others hadn't demanded babies from agencies (and keep doing so), then the market, the industry, wouldn't exist. The NCFA and adoption agencies wouldn't be sinking millions of dollars into research on how to persuade/convince/pressure more mothers to surrender.
Second -- and main reason -- I resent her is that she severely abused my precious child. I feel a great degree of anger about how she damaged and hurt my baby. Why was my child given to an abuser -- oh, yeah, because she had the money to buy a womb-fresh newborn.
Thirdly, this selfish predator had no compunction against taking the baby abducted while the mother was coerced into surrender: drugged, tied down flat, and never allowed by the abductors to hold or see her child. Was that fair, that that was done to me to provide her with an infant to replace the hypothetical one she couldn't give birth to? NO.