I missed connecting Karlach with Dammon (due to not having her in my party until too late).

Is there any way to find him again or is there another solution to her probloem?

if he didn't die in the grove attack or get killed after they leave the grove [both depend on your actions] then he should be at last light inn until the end of act 2... in act 3 he goes to the gate [assuming still alive]

The fact that you didn't mention where you missed Dammon makes me think you're talking about the Act 1 in the grove. If that's the case, depending on your choices you may be able to meet up again in Act 2.

Obviously, the "depending on your choices" implies you didn't make choices that cause him to die.

I don't personally know of another way to solve Karlach's problem other than Dammon, but I've only scratched the surface of what's possible.

Edit: I started this and walked away... and posted it 3 hours late, but I did it without spoilers :)