Without knowing the details of the situation it seems to me that the partner feels she is in the stronger position and is taking aggressive action. There's no future in the partnership for you and your wife, and you should be honestly assessing whether the partner has skills you need or the other way around.
My gut tells me it's your side who needs the partner... she doesn't need you, and she's willing to go out on her own to prove it.
I think you should cut your losses, dissolve the partnership, and start over with 100% ownership. If you and your wife lack the skills or confidence to go it alone, then you've discovered why your partner thinks she's carrying you and doing more than half the work.
Try to be amicable when you split, and position your new business so you are not fighting over the same customers every day - carve out a different specialty. This way you can do joint ventures with the partner in the future by letting her have some space in the marketplace.