Most of the time the baby is the same race as the mother. The exceptions to this happen when one of the parents is a beastkin race and the other is not. If the mother is the beastkin, then the baby will be a halfkin of the mother's race. If the father is the beastkin and the mother is human, demon, seraph, or one of the elves, then the baby will be a halfkin of the father's race.
There have been some mods to allow halfkin to give birth to beastkin, and some weird race genetics. So if you really wanted her to have a mixed race or slime baby, then you might try Ralph's mod.