I understand that mother’s milk is Parev. From what source do we understand this? Is it permissable to use it in preparing meat dishes?

The gemarah in several places (e.g. Kritut 22a) derives from verses in the Torah concludes that human milk is exempt from the various halachot of animal milk. On that basis the Rashba in a responsa (Part 3; 257) writes that woman's milk is Parev in that if it falls into a meat dish it is nullified in any amount, but that one should not cook with it because of "Marit Ayin" that is it could be mistaken for animal milk. That is a rabbinic prohibition. The Rashba's opinion is brought in the Shulchan Aruch (Yoreh Deah 87) as definitive.