Sorry, I don't drop by all that often anymore because the forum is slower.
DiMarie is referring to DAC (Disabled Adult Child) benefits or CDB (Childhood Disability Benefits).
If your daughter marries she will no longer be eligible for SSDI with the one exception if she marries someone also receiving SS benefits, this is called a "protected marriage". (It's rare but it does happen. This rule was put in place to allow two beneficiaries with mental impairments to get married without losing benefits.) If she were later to become divorced or widowed, she would not become eligible for DAC again, the exceptions being a voided or annulled marriage. She could of course still apply for SSI at that point if needed.
Right now she should be receiving 50% of whichever of your SS benefits is higher. She could receive up to 75% of either parent's benefit upon their death.
Disability Planner: Benefits For A Disabled Child
SSA - POMS: RS 00203.015 - Re-entitlement Requirements for Child's Benefits - 04/03/2013
There are special resources for young DAC beneficiaries to help them go to college or receive training and even work part time. If she can take classes online, you might want to encourage that. There are many jobs that can be done from home now. She could actually earn credits towards her own SS record.
Planning for Adult Children with Disabilities – Special Needs Alliance