As I said earlier, that specific contrast makes me cringe. If one group is making a historical reference, other people have the right to debate it. And though it might make for a swell final exam question:
Compare and contrast the movement for gay rights in the United States with the Civil Rights struggle for African-Americans.
It does not work on a simple one to one comparison. I think she - as an African-American woman (among other things) has an absolute right to point that out.
While she may have been (pick one: silly, ill-advised, out-of-line, wrong, poorly informed...) to write the letter, unless it can be found in some way that is obvious to 12 people that it directly and overtly interfered with her doing her job, she can not be fired (from a public school) for doing so. And, since I'm damn skippy that they ain't gonna want this to go to jury in Toledo, they are going to settle out of court for a nice chunk of change.
And I rarely cry when someone offends me. I doubt that most Americans do. They might well give you some equivalent to the middle finger salute for it, but we tend to otherwise not let our feelings get hurt too bad. It's not a nanny state yet.