I think if its anything its Kagome. While she has respect for Sesshomaru, i think its because she's been introduced to him as "Lord Sesshomaru" in a childish mind She probably calls people by what they have told her is their name. Ie. Inuyasha, would be Inuyasha, or perhaps Hanyou, or Half-breed b/c of what Sesshomaru might say, Jaken b/c he has no title, etc.
As for Kagoem, realistically, I think she refers to her as "the girl/woman that travel's with Lord Sesshomaru's brother" or "Inuyasha's miko" i personally understand the manga's too big to look up small detail info. I guess depending on how much you want to make your story canon i would go with something Sesshomaru might call Kagome. As it wouldnt be her name, and he wouldn't call her Lady anything.
thats my 2 cents
-r0o