Some corrections

Comparative Adjetives

When we talk about two things, we can "compare" them, we can use comparative adjectives to describe the differences

you can not say She is not tall than me because in this case tall is a comparative adjetive, you can say She is not taller than me

If you want more information about this you can go to this link http://www.englishclub.com/grammar/adjectives-comparative.htm