Calculating the taxable portion of IRA distributions when you have a traditional and an inherited IRA

I made post-tax contributions to my traditional IRA, so I have an IRA basis. I also inherited an IRA from my mother. She did not make any post-tax contributions to her IRA. I have had to take distributions from her IRA. Are the two IRAs merged together for purposes of calculating the taxable and tax-free percentages of distributions?  Or would distributions from her IRA be 100% taxable?  Thanks.