He will/would meet her when she is free.

Both are correct. The first sentence implies a condition: "He would meet her when she is free . . . if . . ." Without more context, it is not possible so say if it were correct to have used "would." As an example: "He would meet her when she is free, if she were still interested." After a condition, one uses the subjunctive mood (in this case, "were"). It is also used in clauses following a clause that expresses a doubt, a wish, regret, request, demand, or proposal. So, i used the subjunctive mood in the sentence "Without more context, it is not possible to say if it were correct to have used 'would'."--because a doubt is expressed.

Thanks, Setanta.

You're welcome.

I might add that many, probably most native speakers of English don't use the subjunctive mood, and many, perhaps even most of them don't know it is. If you use "was" or "is" rather than "were," most native speakers probably won't even notice.