I have never before heard anyone suggest that contemplative would be so restrictive for clerics of an ideal; in every discussion of the class I have read (and it comes up a lot, being a rather convenient source of a bonus domain), the interpretation is that the bonus domain must be one you could have otherwise chosen as one of your original cleric domains, i.e. one available from your deity or faith, alignment domains can only be chosen by clerics of the matching alignment.
That said, you highlight a discrepancy with that interpretation; it does say a “domain made available by her [...] alignment,” rather than a domain made available by her faith. Strictly speaking, the only domains that your alignment makes available are the alignment domains. So by strict RAW, I believe you are correct, you can only choose the Good or Law domain since “your deity” (that you don’t have) doesn’t make any domains available, and your alignment only makes Good and Law available.
However, personally, I find this an unecessary limitation; yes, contemplative is rather popular for the bonus domain, and yes, that’s an extra feature for an already-powerful class, and yes, it is very easy to get, but meh. The cleric is one of the most powerful classes in the game with or without this ability, but the option of dipping contemplative for an additional domain makes a wider variety of characters possible that otherwise would not be. I call that a good thing, so I would allow it.
It looks to me that the authors of contemplative either forgot that clerics of ideals existed, or assumed they’d implicitly substitute their ideal for “deity” in the rules text. I base this assumption on the very fact that Law is the only choice available to an LN cleric of an ideal under the strict-RAW interpretation, which would make the 6th-level bonus domain completely pointless; when an option might be completely pointless, I expect the text to at least recognize that possibility with “if any” or some such.