Is it normal...to have a 4 year old over active child? Who you know that is only trying to get your attention after she knows that attention now is focused on little sister? From a really well behaved child to a really mischievious child throwing tantrums all the time?

From your description, I think it could be a tinge of sibling rivalry. As you mentioned, she starts to act up when attention is focused on her younger sister. Plus at that age, it's alot about testing limits and boundaries so the tantrums are probably a mixture of both. A friend of mine would get her son involved in getting his little sister ready -- help pick out her clothes or hold the milk bottle etc. This way, he learns that his sister needs the extra attention for now and by asking him to help, he is distracted and feels needed, thus lesser tantrums and screaming matches.

Its normal for toddlers to feel a bit of jealousy towards their younger siblings as they used to have the spotlight.. I am experiencing it at present with my 3 year old son.. What I do is I always call him whenever the baby cries and says, "Be like your older brother.. He is very nice and loving.." Then I'll ask him to talk his little sister too.. It boosts their confidence and mostly gives them a bit of responsibility..