jackdaniels: a good technique to get her in the mood (at least it worked for me) is to bring up some of her favorite past lovers during your lovemaking. Have her show you (with the dildo) just how her favorite past lover used to fuck her. Keep telling her just how beautiful she looks while doing this, and how much you would love to be right there and see her perform with a real bull. Keep assuring her that it's only sex, and no permisteral emotional connections need to be formed with her bull lover.
Perhaps at work one or more guys may be coming on to her...she might fancy one of them...ask her if she would like to go on a date with him and later tell you what happened. When my wife finally went out with a guy who had been putting the make on her, and I stayed home to babysit I thought my mind would explode with anticipation until she got home in the early morning hours. When she came home and gave me the juicy details of her sex with him, I immediately got the dildo and told her to show me just how he fucked her. She told me he had made he cum about 5 times that night. I then just about ate her alive!!! She loved what it did to me and how hot it got me, so much so that she was from that time on totally sold on the idea of cuckolding me again.
Good luck, and keep us posted!