When my mother passed in 2010 - I had to file her taxes individually for that year. Once that's completed, the IRS will know that that tax payer is now deceased.
So, if your mother passed in 2018, you have to file her taxes as she normally would, you just answer deceased at that question. If I remember correctly it'll ask did the tax payer pass during 2018?
I would also encourage you to contact all three credit reporting agencies and inform them also of her passing so they can close her credit file. You'll have to provide them with the death certificate.
I am sorry for your loss -- and I hope some of this information was helpful.
