I suspect the tourist visa might be the only way to go, but I really don't know. What I do know, however, is that in December of 2009 they changed the entry policy for tourist visas. If you are on a tourist visa to India if you leave the country you cannot re-enter until after two months have passed, which if she's planning on staying with you the whole time, she won't be able to re-enter for a couple of months. (People used to just hop over to Thailand for a week and then come back because on an Indian tourist visa you can't stay more than 6 months at a time.) Though this has been quite controversial here, but I suspect nothing will be done about it in time to do any of us any good. I hope this is a little useful to you!
On another note about partners, does your dependent need to be an American citizen as well, or is that irrelevant for dependent allowances?
Cheers!