It is certainly your decision on what too old is to be nursing. I night weaned my son at about 16 months b/c I was pregnant with #2 and desperately needed sleep. He had no problems night weaning at that point.
He was a comfort nurser and wanted mama and the closeness more than the nutrition at that point.
I don't know. I personally think your daughter is too young to wean. My son didn't eat much at all til 14 months. He tasted food and I didn't intro cow's milk til well after 12 months. I sort of am one of those "crazy" people who think baby cows should get cow's milk and baby humans should get mama's milk.
There will be people who tell you to stop nursing and let her cry. She will eventually learn that mama won't come to her and she will stop. But, do you want her to stop b/c she doesn't need you as much (maybe in a few months) or stop b/c she's found that adults aren't reliable or trustworthy?
You said her cry sounds like "something is bothering me". Maybe it is, maybe she still really needs that closeness to mama. Are you working? Or spending less time with her during the day perhaps? I know my son nursed more at night the days that I worked. He wanted the closeness.
Good luck. There are as many answers as there are posters on here. Only you know what's best for you and your family.