Learn English – What does “muster through” mean

The usual meaning, as Mick suggests, is to live the life one wants to have through close involvement in someone else’s life. It’s commonly used to talk about parents who had ambitions that didn't go as far as they wanted, and are pushing their children to achieve similar things so the parents can feel accomplished. It can also be used for any other case where one person’s desires are satisfied by making someone else achieve them.

There are two components to this phrase to break down.

come through:

1. [for someone] to do what one is expected to do, especially under difficult conditions

With regards to in the clutch, we have to look at the definition of clutch. In this context, Darry is using it in the same way it is often used in sports. In sports it is often used to describe players who can make the best plays even when the pressure is highest. For a person to be good in the clutch means to be able to perform in those critical moments, regardless of the pressure or stakes riding on the outcome of the game or match they're participating in.

So just taking in the clutch on its own, it means those moments where the stakes and the pressure are at their highest.

Combining these two definitions, to be coming through in the clutch means that Trisha has followed through and helped Darry, right when he needed it most.

However, before Darry says this, Trisha drops him when they're confronted by rats. This is the opposite of being clutch, so Darry is likely being sarcastic in his comment, saying that Trisha choked under pressure.