I think you will find they are both female. Dominant behaviour, which is what treading is, displayed by one female over the other in the absence of a male, is normal, and does not mean that one female has changed sex, or that a male is laying eggs

On the other hand, if you see the whole whangdoodle, corkscrew or whatever, during treading, then you have one male and one female who lays a lot of eggs

No need to tip them, just observe the action.