Stigma, and in particular self-stigma, is still a big problem for volunteer responders. Being strong, a fixer, someone who helps others, is often a big part of how they seem themselves and how they’re viewed by others.
When they get psychologically injured and become unwell, the shame and confusion they feel about this happening is often as big an issue as the injury itself. For some it is the main issue, as they experience a collapse in their sense of self.
Remind them that we all have mental health and responders are not invincible. Show them the films on this site of other responders talking about how self-stigma affected them. Encourage them to talk to colleagues if and when they can. Use (and persist with!) self-compassion strategies to challenge self-criticism, asking them how they would treat their best mate if they were struggling. How they would talk to them, encourage them, support them.
The same responders who found it difficult to ask for help can become passionate about helping others once they’ve benefitted from support. Finding ways to act on this, to give something back, can be an important part of their recovery. If the person you're supporting takes on this role, remind them to take care of themselves. It can be hard once they've become a mental health champion to ask for further help if they need it.