She is waking, intermittently... BUT has not had... a full, nap. And is still groggy/"sleepy" at this time. Not FULLY awake.
Thus, when you go in there it then actually wakes her. And the cycle of sleep phases.
Per my kids, they also did this.BUT when they had not had a FULL nap. It was just an intermittent waking. Thus they wake, not in a nice mood. Or they are startled awake, before they have had a full, sound, nap.
BUT, if I (per my son), let him be... he would then fall back asleep.
His was not an emergency screaming fit, type of waking. But a jostle in their sleep cycle and rhythm.
I knew, his sounds.
But if I had gone in, and "interfered" or began talking to him or "waking" him, then he would wake, very, not well. And crying.
BUT your child is also 1 years old... AND this is ALSO a time, developmentally, in which they may have "night terrors" during sleep. This is not only at night. And you cannot control this. Read about it online.
My kids began having that from about 1 years old. For my kids, their night-terrors was at naps and/or night time. And at this age.
You should and must, ALSO tell the Sitter, about your child... and her nap routines... what you prefer... and, that she is going through night-terrors, etc. A good seasoned Sitter, will understand. And know, about developmental aspects.
AND if you want your child to nap at certain times, and in a certain routine, you must tell your Sitter this. So that, the sitter does not, undermine the routines you have for your child.
Remember, you are the parent.
Next, remember all kids cry and/or go through developmental stages and phases and separation-anxiety. And no Sitter, will expect your child to be 100% perfect, non-crying, everyday all day.
That is not, rational.