How do you write 'sha' in katakana?

Question:

I've recently started learning Japanese, so naturally I'm learning kana. To practice katakana, I write peoples' names and remember what they look like. The annoying thing is, I cannot write one name because there is a 'sha' sound in it. I am aware of the combination sounds you can get in hiragana like kyo and jyo, but can you do it in katakana? I know that 'Shooter' in Black Rock Shooter is something like chi-oo-ta, so would I have to do chi-aa? Would that work? The name is Alisha, btw.
Thanks
x
P.S Any tips for remembering kana?

Answer:

All hiragana can be kanakana, and vice verse.

The key to understand is vowel (a,i,u,e,o).
あ、い、う、え、お
ア、イ、ウ、エ、オ
A、I、U、E、O

さ、し、す、せ、そ
サ、シ、ス、セ、ソ
sA、sI、sU、sE、sO

しゃ、しぃ、しゅ、しぇ、しょ
シャ、シィ、シュ、シェ、ショ
shA、shI、shU、shE、shO

Shooter = しゅーたー = シューター (shu-ta-)

Alisha = ありーしゃ = アリーシャ

You might want to check this site to master kana.
http://memorize.com/japanese