Why does our refund go down by $1000 after claiming the disability tax credit for our daughter? The refund should go up, shouldn't it?

In theory you are right claiming the disability tax credit should improve your tax situation.  A couple of considerations 1) ensure the right person claims the tax credit if you are doing with your spouse, 2) have you first submitted the t2201 form?

https://www.canada.ca/en/revenue-agency/services/tax/individuals/segments/tax-credits-deductions-per...