"Lisa had never had so much time to herself in her life, it gave her a lot of time to think, time to meditate." This really should be broken into two sentences (after "life"). Other than that, nicely written.
"Please let him be ok! She thought to herself." "She" shouldn't be capitalised.
I like the plastic cup scheme. Very intelligent, and feels exactly like the kind of thing Lisa would do.
"She could, of course, just assume that sleeping took eight hours, but that would be tantamount to admitting defeat. No, she would solve this." Another sentence that feels very in character for Lisa.
Typo: "Ce'mon" should obviously be "C'mon".
Apart from the lack of punctuation, funny line! Made me chuckle."you're getting paranoid, a symptom of boredom I do believe"
I think "simply" isn't needed here; it adds nothing that we can't already imagine from his dialogue.He stated simply
The toothpaste idea is, again, one of those smart ideas Lisa would definitely have. Her worrying about her sanity is in character, too.
OK, sorry to be harsh, but you don't do this in prose. You either rely on your readers to know who Juliet is (which is a fair assumption; she seems to be a reasonably popular character, and I've heard of her, despite not having watched the episode); or, at most, you write "her friend, Juliet". Or if you're really worried we won't know who it is, you have an author's note before the start of the chapter (and well separated from the narrative itself) saying something like "the 'Juliet' mentioned in this chapter is Lisa's friend from 'Lisa the Drama Queen'". The one thing you don't do is to put explanatory notes in the middle of a story."And you said I was crazy." Teased Juliet from next to her on the bed (Lisa's best friend from 'Lisa the Drama Queen')
Apart from that, I like the bit with Juliet a lot, despite not even having seen that episode, which shows you must be doing something right.
"Another thought hit her suddenly crushing her joy." This needs a comma after "suddenly", and truth be told, it's a bit melodramatic. Not awfully so, though.
To be continued.