MY 24 YR OLD BUSTY BLONDE FIANCEE AND HER BBDILDO

We've been together for almost 7 yrs and recently I purchased her the Sean Michaels dildo. She wasn't suprised by the size about 10 inchs in lenght and another 7 in circumfrence as I have bought her others around about the same size but they were realistic white ones. She never realy took to the white ones but openly admits that the new black one is her favorite. She wants it all the time and is her go to toy to make her cumm. She talks so nasty as I pump her full of the bbc and cumms like crazy 2-3 times in a 20 min. session. I love the way she feels after and she is turned on by this. In the past she would ask me to give her the dildo as if it was cumming inside her and she recently ask me to do this with the bbd and she went crazy having the longest orgasm I had ever seen her have. She takes almost all but an inch of this dildo and it gets easier and easier every time we use it. My goal is to get her to use the even bigger Bam dildo that I've already bought. She knows what I want but is intimedated by the size of it. Any tips would be greatly appreciated. Should I wait to see if she asks for the new bigger blk dildo on her own or how should I introduce it to her? She realy acted scared of it at first but the more I use Seans blk dick in her the more excited she seems to get not to mention stretched out. It would just break my heart for this amazing dildo to be to big for her and her not want it at all. Help me what do I say or do to make this happen?