Be dead Boring... or be dead Excitin'

What words does Rita use to express her enthusiasm for Macbeth?

"... I thought it was gonna be dead borin'..."
"... But Listen, it wasn't borin', it was bleedin' great, honest, ogh, it done me in, it was fantastic."
"... It was dead good. It was like a thriller."
" I just thought it was a dead excitin' story."

Rita was so delighted with the play, she felt so happy about her discovery, that she was eager to write an essay and tell Frank how did she feel. It was a completely new experience for her and the fact that she enjoyed the play promoted or encouraged her with the writing of the essay.

Could she use these words in an essay?

Of course she cannot use these words (read above) in the essay. This is colloquial language and she should use formal language do an essay.

Make a choice and Resign to something

What expressions does Rita use to emphasise how important the course is to her?

Rita claims that the course provides her with life. She feels satisfy, she is very happy with the course and she wants to keep doing it.
I think it's reasonable and maybe predictable that Denny, her husband, gets jelous. When somebody starts doing something, such as taking a course, job, or any kind of activity the people around him/her may fell neglected or rather abandoned. And it's true when we make a choice we have to resign to other things, and sometimes resign to spend time with people we love. What is more, Rita seems so excited about her carrer and her teacher that makes a good reason for Deeny to be jelous.
Although she is right to be angry with her husband actitud and the fact that he burned her books, I agree with Frank that they have to talk. If she is so happy with the course she has to do it and he should suppot her.

"Comin' here, doin' this, it's given me more life then I've had in years, an' he should be able to see that."

What doesn't kill you, makes you stronger

Why do you think Rita says 'it makes me stronger coming here'?

As Edward George Earl Bulwer-Lytton said "the pen is mighter than the sword". I believe that knowledge is "power", knowledge not only opens your senses and helps you to see and discover things, but it also gives you a kind of power, which nobody can steal from you.

Rita is immersed in an emvironment where life is very simple. Her duty is to work and spend time with her husband and friends, that's all. She is inside a vicious circle.
People are there to live, not think about life or anything. The fact that Rita wants to learn will help her to change her environment (if she wants) will help her to think about other realities, even when the people around her don't like the idea that she can change her way of thinking, living (and maybe leave them).
Learning opens people's minds, learning empowers people. Knowledge makes people feel stronger (other people cannot deceive them).

I think this situation is repeated many times in the entire world. Just as an example, George Orwell's "Animal Farm" just crossed from my mind, where ignorant animals are deceived and controlled by those who knows a little more. They are deceived because they cannot read.

What I learn from you about art an' literature, it feeds me, inside. I can get through the rest of the week if I know I've got comin' here to look forward to.
Denny tried to top me comin' tonight. he tried to get me to go out to the pub with him an' his mates. (...) They hate it when one of them tries to break away. It makes me stronger comin' here. That's what Denny's frightened of.