By now your Evica must be 7 - 8 months old. By the time she reaches 1 year old, you may notice her body to become fuller, however, she will not truly grow in height.
We have talked about this before, the overall size of a budgie is determined by their genetic inheritance. If one or both parents have a smaller frame and build, then their chicks can be smaller in size as well.
Even though your Evica is a bit smaller, that doesn't mean that she is weaker or not healthy, this is not cause for concern.
From your description, it seems Evica has more of a shy personality and that's why she doesn't sing as much and is not as outgoing as Dobrica.
Some budgies are naturally more playful than others, this also depends on their personality traits. If Dobrica is playful, then he can teach Evica to play.
When it comes to forming a good bond with your budgies, it's important to read their body language and to respect the safe boundaries set by them.
Most budgies when get past the baby stage don't like to be petted and this is something that needs to be respected or you will run the risk of having a setback in the taming due to a breach of trust.
For shy pet birds, it usually takes more time to gain their trust and to make them feel truly confident and comfortable around us.
You can use the bond you have with Dobrica to your advantage.
Once Evica sees how happy and comfortable Dobrica is when spending time with you, she will realize you are not to be feared and with time you will notice an improvement.
For all the detailed information on how to improve the bond you have with Evica, be sure to read the information on the stickies at the top of the Taming and Bonding section.