i wouldn't suggest housing them together at all, especially given that they are opposite genders and two distinctly different sizes.
they could breed too early resulting in costly vet care, etc. if one animal gets sick you won't know which one, if one animal gets sick it could transfer it to the other one and then you've got two sick animals. behaviors we perceive as "cuddling" are actually one snake dominating the other. they will compete for hiding places, basking places, etc.
i've heard of experienced keepers keeping them together but i still dont think its a good idea. especially as you seem like a newer keeper. I'd keep them separate.
And as for the hissing, is it possible she is starting her shed cycle. a hissing snake is not necessarily an aggressive snake.. i know a guy with an 8 foot female BCI who "hisses" a lot, its just what she does, no RI, no aggressiveness, nothing.