In 2017 your mother got a $6,350 standard deduction, plus a self-exemption of $4,050, along with an additional $1.250 because she was over the age of 65. That was a total of $11,650 of her income that was not taxable on the 2017 tax return.
Now for 2018 there is no more dependent or self-exemption. She only gets the standard deduction. For 2018 the standard deduction is $12,000. So compared to 2017, that's an additional $350 of her income in 2018 that is not taxed. So my guess is that for 2018 her income increased quite a bit, or she didn't have enough itemized deductions in 2018 to decrease the tax liability.
Now I don't know if in your specific situation the assisted living costs qualify as a medical expense. But if they do, then be aware that the total of all medical expenses must exceed 7.5% of her AGI in order to be included on the SCH A. That's lower than the 10% requirement for the 2017 taxes. I suspect either you did something wrong on her return, or it very well could be that things aren't being calculated correctly by the program because the IRS has not yet released all the 2018 forms you may require for that specific tax return.
