Hold up.
An onee-chan you say?
Is another fox girl gonna appear later?
I believe this is the 'auntie' she's texting in chapter 10. Kagome calls her Onee-chan when thinking about her, but when texting the other fox says 'Tell your Oba-chan' and Kagome calls her 'Oba-chan'. Oba-chan can mean any older woman, and you can call someone Nee-chan who's not your actual sister. So the actual relationship is still up in the air except that it is an older fox lady.
And yes, a whole lot more foxes showing up real soon - chapter 20 has Goro visiting her fox village in another triple length chapter (split into two).