Freedom of speech, freedom of expression.
Some works of art are downright offensive but it's tough to get around their right to create it. At least Cow Lady didn't create a cow that glorified terrorism or pedophilia.
The right to "create" it or the "right" to exhibit it on public property in an event coordinated with civic dollars?
They have every right to create it. The ACLU has no business in telling a community they "have" to include a cow.