|First - good luck!
Poison ivy is a woody shrub (vine). While a somewhat fragile plant in that it can be crowded out by other more aggressive plants, it is pretty tenacious and can be difficult to kill. Any herbicide rated to kill poison ivy would likely kill the blueberry bush as well.
You might consider mixing up a somewhat milder herbicide like RoundUp (not the new RoundUp Poison Ivy) and doing targeted spraying. You'll want to be very careful in and try to spray only the leaves of the poison ivy plant. This will take repeated applications over time since you won't be able to spray liberally. My husband used this method when with some success but it does take time.
Another option is to hand pull the poison ivy plants. I've done this when I wanted to save the other plants and bushes. It is possible to eradicate poison ivy and not actually come in direct contact with it. You have to suit up though and have the right gloves. Gardening gloves would not work - I use PVC coated chemical gloves. You'd want to wash up very well afterwards.
Hope this helps.