I just began receiving SS retirement benefits. My daughter is on SSDI (she has been disabled since birth) and has been added to my record. She has a job and is currently in her Extended Period of Eligibility where her average earnings have a monthly limit.. My record awards her $1249/m, with $756 will coming from her own SSDI record and the remaining $493 coming from my retirement record. My question is, now that she is on my record, if she earns above her monthly limit and losses her SSDI eligibility will my record cover the money she lost when she lost her SSDI? In other words, will she always receive $1249/m regardless how much money she earns at work?
No. The same earnings rules apply to both disabled adult child's (DAC) benefits and Social Security disability benefits (SSDI). You first get a 9-month trial work period (TWP), after which benefits continue until the person performs substantial gainful activity (SGA). If the person does perform SGA after their trial work period, their period of SSDI and/or DAC entitlement would be determined to have ceased and their benefits would be suspended if the SGA continues. However, the person's benefits can be reinstated during an extended period of eligibility (EPE) that runs for at least a 36 month period following the end of their TWP. During the EPE benefits can only be paid for months that the person earns below SGA level (i.e. $1180 in 2018), and their entitlement is terminated if they perform SGA after the end of their EPE.
However, your daughter's TWP for DAC couldn't start any earlier than her first month of entitlement to DAC benefits. So, assuming that her DAC entitlement started after her SSDI TWP began, it's possible that her DAC entitlement could continue even if her SSDI benefits are suspended or terminated due to SGA. She would get her full DAC benefit rate if that occurs, but if she performs SGA after her DAC TWP is completed her DAC benefits could be subject to suspension and/or termination just like her SSDI benefits.
For more detailed information on the work and earnings rules that apply to SSDI and DAC benefits, refer to the following Social Security publication: https://www.ssa.gov/pubs/EN-05-10095.pdf.