Wow. Well now you know why she was available as a "roommate"!

I suppose you could worry that she might leave you if she finds a better deal, but i think you could replace her a lot easier than she could replace you. Women outnumber men like ten to one at our age.

She was probably trying to tell her sister that SHE was not the burden, and that her position was secure. Her sister may have been threatening or belittling her.

You two have been together a fairly long time. I guess the question is are you each or both generally happy?