I wonder if there is a branch of feminism which has taken up the cause against sex-selective abortion?
All branches of feminism are against infanticide, and many are against sex-selective abortions. However, most western feminist groups are unlikely to make it the center of their activism, as it is not a large problem in the west.
One example of a feminist speaking out against infanticide as well as sex-selective abortions is Emma Watson, Gloria Steinem also mentions female infanticide as a problem.
Regarding the apparent conflict of supporting womens choices and access to proper medical care and the opposition to infanticide and sex-selective abortion: There isn't really one. It is possible to support access to abortions, while also criticizing those that use it in an unmoral way (obviously; the same thing eg happens with guns; you can legally own them, but shouldn't misuse them). In my experience, the discussion about selective abortions happens more often about the rights of disabled people vs the right to abortion (at least in the west), but that would be another question.
Wikipedia summarizes Mary Anne Warren - a Feminist and supporter of the right to abortions - , who holds a similar idea:
Warren (1985:104) argues that there is a difference between acting within one’s rights and acting upon the most morally sound choice, implying that sex-selective abortion might be within rights but not morally sound. Warren also notes that, if we are to ever reverse the trend of sex-selective abortion and high sex ratios, we must work to change the patriarchy-based society which breeds the strong son preference.
The feminist website The F Word argues similarly that instead of restricting abortions, the underlying causes should be fought:
I think we also need to recognise that, with regards to female infanticide, the underlying issue is sexism, not access to abortion. Stopping women accessing legal abortions will not stop female infanticide; but challenging sexist social and cultural beliefs may very well do.
The paper A feminist analysis of female infanticide provides a perspective from Indian feminists:
Female infanticide and female feticide represent serious social problems in India. However, these issues also create much debate over a woman’s right to choose whether or not to have a child. While women in India do have the right to terminate a pregnancy, there are several legal stipulations that make having an abortion less about giving women rights, and more about controlling women’s reproductive capabilities (Menon, 1995). Women often do not choose to have sex-selective abortions; instead their husband and his family pressure them into aborting unwanted female fetuses (Kusum, 1993). Thus, while abortion is legal under specific circumstances, it is often used as a way to selectively breed male children who are preferred in Indian culture. Therefore, many feminists see abortion rights in India as contradictory to feminist discourse because abortion rights are not being used to liberate women, but to re-enforce the cultural preference for sons (Menon, 1995). [...]
While the feminist discourse on abortion advocates that abortion is a right over one’s body, sex-selective abortion in itself is a form of female violence.