Go and visit. It will make her happy.
Would you appreciate a visit from some relative who couldn't be all that bothered to come and see you until you found out you had terminal cancer?
PS. This advice is worth what you paid for it.
Everything else has been said - It seems to be important to your husband , this is good enough reason to go .
Go and see her. You may be able to help her in some way. You probably feel like you would be treated as an impersonal in-law. BUT she has treated you and your family with thoughtfulness and love.Get in the car and get yourself to see Aunty.