There are two solutions to this. Amanda and Jessica could borrow the money. Of course it isn't easy for small companies to get a business loan. Banks are cautious and don't lend major amounts of money to small businesses. Plus, the loan must be repaid, with interest!
Another alternative is to issue "shares" of the company. This would allow people to buy a small portion of the company.
This way they wouldn't have loans to repay. The money they raised by selling shares of stock would allow the company to expand. Not only that, they'd even have enough money left over to build up a reserve, so they have extra cash in case of an emergency!
There are drawbacks to this, of course. It would mean Amanda and Jessica would have to share control of their company with their co-owners, the stockholders. They have to keep the stockholders informed of company performance and future plans.
Most importantly, they have to keep the stockholders happy, which means making profit! If the company doesn't make the profits the stockholders expect, Amanda and Jessica could even be fired from the company they started!