First please accept my condolences on your recent loss. The financial stress must just be making this worse. In WA, most tenancies are "joint and several" which means that each of you is obligated under the lease, not just all three of you.
Your landlord is being a stinker, don't get me wrong. But they can do this. They can demand that you pay the same rent even with only 2/3 of the original tenants being there, and they can evict you if you don't pay it. Their lease-break fee seems excessive but a court could agree with them, and the risk is that you would then owe attorney fees.
Another option you might consider is to see if you could find another co-tenant and get management to approve that person moving in with you and your daughter. Be sure to get approval first.
Hope this is helpful. Elizabeth Powell
I'm very sorry to hear about your mother.
My question would be whether it was only your mother who signed a lease or if you or your daughter signed it, too. If you didn't sign anything, it might at least be a bargaining point in your negotiations with your landlord. It might be worthwhile to check the language of the lease in particular.
Hope this helps.