Why do people talk like a baby to the elderly?

maybe someone can help with this i have a 90 friend that is staying with me and now for the last few weeks her voice has changed and almost sounds like a child and if i say something to that fact she puts her fingers in her mouth like she is being punished what can i do about this

She is very close to our dad. and she is single. When the other sisters go and visit, me included, we aren't seeing the crying and the hysterics or even having a normal conversation like she says she does. He mumbles and stares at you like he doesn't recognize us. When my sister went to counseling she came out of it by accusing the therapist of using her as her therapist. I don't know anymore. She really does need some help. When our mom died she had read a passage she wrote and in it she told our whole family that she hurt more than anyone else. If you knew our family history your mouth would have dropped. We can't seem to make her understand that dad needs to stay at the nursing home. Noone is capable of handling the care for him at home. My other sister passed away this past November. I was not able to get closure. The last time I had seen her was at our mothers funeral. Needless to say we had a fight and didn't speak. She died without us talking about it. I have my own cross to bear and "Teri" finds it up to her to put her two cents in about it. Hopefully she can snap out of it. When our father does die, it will be a horrible, excruciating experience for all of us. But I feel that may be the one thing that sets her off her fate.

My guess is that her constant attention and time spent with her father is taking its toll. Her best intentions in trying to make sure that her father is well taken care of are causing her to over react. She has a very strong attachment to your dad. Perhaps she is single and the fear of losing her dad is so strong because of losing the strong male in her life? Or maybe she has always had a very strong attachment to her dad and this is just a continuation. People deal differently with these things. But it sounds like she is heading for a breakdown if this continues. Is there a counselor in the home that can speak with your sister? A case worker?