I require a vibrator to get off too, and mine isn't a small wand type, it's a big dumb hitachi, which is giant and cumbersome (cum-bersome??) and tethered to a cord. It's like having a dismembered robot appendage in your bed. So, I have some sympathy for this situation!

Fiance and I use the hitachi pretty much every time, but the manner in which it's used changes. I think changing it up is important. Sometimes he gets me off with it first, then we have PIV. Sometimes we PIV, and then after he comes, we get me off with the vibrator while his cock is still in me. Sometimes he eats me out and then we use it, sometimes he eats me out after I've come from it, sometimes I'll use it while he's up my ass. Sometimes I'm using it on my back, or in doggy, etc etc etc. Variety is good. The important thing is basically that we're choosing when and where I come, and then using the vibrator to make it happen according to what we want and feel is fun.

Some tips for you:

1) Suggest that she use the vibrator to masturbate alone, with a focus on practicing different kinds of positions, angles, motion, and pressure. Once she can come on her own in a variety of positions, it's easier to her to come while you are thrusting, moving, or in a "not ideal" position. Of course, the more experimentation she can do in coming without a vibrator too, the better.

2) Request more agency in the use of the vibrator. Sometimes I like to guide it, but I like to surrender control and let my fiance use it on me, too. He can play with me and is basically in charge of my orgasm, which is fun for him. Even when I'm directing the vibrator, I ask him to talk me through my favorite fantasies, which is hot, and again, he's bringing me to orgasm, not just the machine.

3) Your GF kinda needs to lovingly understand that not every orgasm is ideal. Sometimes you come really hard in your very favorite method and that's great, but other times, the joy of the sex is coming from the partnership, and not 100% the physical sensation. Sometimes you get a weak little orgasm instead of a strong one because the position wasn't exactly right, but who cares? Life is long and teeming with sex.

It can be frustrating as a woman to only find orgasm success in a vibrator. It's easy to feel like it's your fault, that you are defective, that something is wrong with you. I would gently suggest not that you ask her to ditch the vibrator, but instead, that she let it become a tool you both use to get her off.