How could Maddy pay the credit card bill for a Hawaiian vacation when she hasn't left her house in 18 years?

How did Maddy, who hasn’t left her house in 18 years [intend] to pay what must be a humongous credit card bill?

^{variety.com - Film Review: ‘Everything, Everything’}

During the movie Everything, Everything, Maddy applies for her very first credit card, which she then uses to purchase...

• Clothes to replace her previously white-only wardrobe. ($50 per outfit) = $250
• 2 plane tickets from Los Angeles to Hawaii ($400 each) = $800
• 1 weeklong rental car ($20/day) = $140
• A yellow one-piece bathing suit ($30) = $30
• 1 weeklong rental house for her and Olly ($100/day) = $700
• Scuba diving tour + equipment ($200) = $200

Considering Maddy is trapped at home and has no source of income, is it ever explained how she could pay off her estimated $2,000 credit card bill?

If not in the movie, is this possibly explained at all in the original novel?