I don't see how that would be remotely possible. You shouldn't have anything to worry about. While IUD/IUS's can become dislodged on their own, it's rare and usually only happens fairly soon after insertion, when the cervix may not have resumed its normal duties. Other than that, it would take a pretty good tug to move it.
Given the gradual action of a pump, she would most definitely feel it begin to happen before it actually came out! And that's assuming a pussy pump could achieve that at all, which I'm confident in saying it could not. Even if you were to put a pump directly over the cervix, I'm pretty sure nothing would happen.
Remember that the vagina doesn't gape like the mouth of a cave; the entrance is less an opening as it is an introitus - that is to say, when nothing is holding it open, it is essentially collapsed in on itself. So while the pump may, depending on how big it is and where it sits, suck out any air that has become trapped in the vagina, this would actually have the effect of tightening it, like a vacuum-sealed pouch. The vaginal walls would be 'shrink wrapped' around the coil's strings, holding them in place. If anything.
But that's all moot, because the pump simply doesn't have the continuous suction required to even begin to drag the strings out. In order for suction to continue to increase, there has to be air to suck. Once you've achieved a seal, that's it, it doesn't keep sucking, it just holds. Even if you don't have a perfect seal, the air getting in will most likely be from around the edges, so again, it won't be pulling the strings.
If you are still worried, try pumping, then release it, then you or your wife put some fingers in and feel where the strings are. I'll bet you they'll be tucked up near the cervix still - that's where mine always are. And again, even if it did happen, it wouldn't happen all at once. She'd be able to feel the strings straighten out and go taut, then the pressure on the cervix after that. Plenty of time to stop long before the point where it would potentially become painful or actually dislodge the coil.
So I don't think you have anything to worry about. But it is always good to ask whenever you have a concern. :) If you still have your doubts, DO ask a professional.