Oh it'd be every bit as much their decision. Truth of the matter is that several of her current bulls would be eager to knock her up (God knows they get plenty of practice at it).
Now after she had the baby it'd be a different situation. I know we wouldn't need any financial support from the bull, and his level of involvement in the ******* upbringing would be something that we would all have to coordinate. That's if we selected one particular individual to be the stud in that scenario.
More likely she would be getting filled with cum by several bulls, as she is now, so we wouldn't necessarily know whose kid it was without ******* tests. So really I guess there are two different methods for her to be bred. One where a single bull is selected for her to breed with. The other where she continues to accept creampies from all of her bulls as she does now, sans the birth control, with all parties being aware of the possible results, and all bulls willing to remain anonymous as the potential *******.
I don't know which method we may end up doing but I know that they both sound great. And no this isn't just us fantasizing. This is something that we will likely do in the future. She and I will likely make our own baby first, but after that it's all black breeding unless I sneak another in there somehow, heheh.