The only way I know is that you have to talk to her about the research, then talk about the chastity cage (forced), agree to the procedure and go through this storyline. Towards the end, if you refuse to wear the chastity cage, you will have what you are asking about.
You can do the discipline experiment or there are 2 chances where you can force her to have sex and if you are lucky she will get pregnant (btw the 2 times you force her you can try and wait until she is in heat for better odds)
