I'm with N2L on this one. When I read the original post I thought "Oh no, no-one but me would be taking my DD to swimming lessons!" If not me, then DH. Admittedly I felt a little stronger about it as I imagined her in the water with my DD, as she's younger and can't swim on her own. But still, things like this are, to me, bonding times between parent and child. I wouldn't be comfortable with someone else doing this, especially my ex's gf of less than a year.

For me, the fact that she'll have a three week old bub makes no difference. What she does and where she goes with the bub has nothing to do with me. But I wouldn't like my child's father deciding he wants her to do swimming lessons and then giving responsibility of it to his gf (who, btw, I wouldn't consider to be a step-parent yet).