Hi Kenny!
I'm gonna take a guess that you are a mid-late teen and the young sister you are interested in is at least 20. Talking in general terms if "Abby" is doing a demonstration at an assembly then she is likely a pioneer or someone in very "good standing" in the circuit.
She will quite possibly be looking for no one at the moment but if she is it might be a "spiritual man" to marry and serve as a pioneer with. If she is as pretty as you say then at this moment she will likely enjoy having the attention of men older than you - perhaps her age or even mid to late 20's. They may well be Ministerial Servants.
The fact that you are 4 years younger than her and newly baptised goes against you because you will be viewed as a spiritual "babe" - especially if you are not pioneering.
As Londo said - she is not interested. Honestly, you would know.
I am very old now - in my fifties but I remember at age 18 having an amazing crush on a 17 year old who was a lovely very pretty young girl at the time and who has grown up to be a lovely lady who is married with grandchildren now.
She was kind and went out with me to the cinema and sports centres two or three times but it was obvious she wasn't attracted to me like I was to her.
My heart was aching - I literally cried myself to sleep at times such was the intensity of my feelings.
Soon she found her husband to be who was five or six years older than her and who is a really nice guy - he just was more mature than me as you would expect and she was into him.
A couple of innocent (I was a believing devout JW at the time) girlfriends later I met my wife to be. I still have fond memories of the girl I had intense feelings for but you will get over it even if it feels like forever now.
My advice looking back? Put any excess energy into making yourself employable and better educated.
When you are a bit older you'll find good relationships if you have honest decent intentions not to take advantage of women but to love them and be loved back.
Take your time to really investigate the history of Jehovahs Witnesses and ask questions here; we really want to help.