So, that leaves you with she might not want to....or you two simply aren't working it quite right? Ha, sorry, just the images that pop into mind.
First, I am by no means an expert, but I am a woman. I've only once been able to 'deep throat' a man -- If by this you are talking about when he goes past the gag reflex and a bit farther or are you talking porn sex BJ stuff?
If the first, than I've managed it once. If the second I think they make that stuff up.
Let's see, for us, he was far enough in my throat that I didn't need to swallow, his cum slipped down my throat without filling my mouth, too. It was hot. I really loved this guy. I mean, really, really loved him. We were open about sex -- what we wanted, what turned us on, and so on -- this made it so much easier to try things out. His favorite was the BJ. Shrugging here, my favorite was everything! lol.I think he might say his was everything too, but I like giving, so....anyway, long story short. We had a great relationship, which made trying to get to the point of deep throat fun. We finally managed it one day-- I'm sure by sheer accident because I've never done it after. I was on my knees, he was standing, and I tipped my head way back, his cock simply slipped past my gag reflex and farther down my throat. Not sure how much farther, but it was hot. Not sure how this helps, since this seems the most logical way (to me) to press your cock down a woman's open throat. The bed idea sounds like it might be too much of an angle and a bit uncomfortable.
And, yes, he was big. I have no idea how big. He wasn't 'girthy' like as big as your wrist, but definitely a challenge. He was long, but again, I have no idea how long.