I'm not sure of a hammock that would give you a truly comfortable lay with two people over night. I have however seen this discussed a few times.
If she is comfortable in her own hammock as long as its under the same tarp, your just gonna need a big tarp. I saw luke and his girl both setup under the HG Winter Palace, probably the biggest tarp ive ever seen. So I know it can be done, you just have to find 3 trees in a nice triangle pretty close together.
Look into large tarps, Old Man Winter seems big enough to get two hammocks under but I havent tried it.