Yes, it is appropriate to use "had had" and no, it's not redundant.
Have and its past tense and participle form had can have two equally valid uses -- as a main verb [as in "She had a bad headache earlier"] and as an auxiliary (also known as helping) verb [as in "She had given him more than enough chances already"], where the verb had is the "perfect" auxiliary verb to the main verb gave, seen in its participle form here, given.
Ok. Good. So what?
Well, it turns out that once in a great big while it is possible to use the main verb have simulataneously with the auxiliary verb have and to say something like "had had."
That is perfectly fine. Honest. Really. However, the reality is that many people think that such a construction is not euphonic (even though it is perfectly grammatical) and therefore avoid it.
Hope this helped you out.
