Aw little Asenka is gorgeous! Congrats!
As long as she's feeding at the correct size (as others have said prey size no more than 1 & 1/2 times her widest point) and seems healthy then there is nothing wrong with her size.
My Corn 'Nagini' is 21 months old and feeding fine on correct size prey, but she looks smaller than an average yearling! I was worried and took her to a vet as I was concerned. They told me that they all grow at different rates and not to worry as long as they are healthy.
Hope that is some reassurance to you.
Enjoy your lovely new snake!