I agree that it's up to the landlord, as normal wear and tear from your tenancy is to be expected. Extra wear from work she ordered isn't. But you can get rolls of clear plastic sheeting that's specifically to protect carpet at places like Joann's, Michael's, or Wal-Mart. They sell it by the yard on big rolls. It has spikes on the back to dig into the carpet and keep it in place, so it's safer than slippery plastic sheeting. You can use any number of coupons or cashback offers to keep the price down (the Joann's app, Wal-Mart Savings Catcher, Ibotta, topcashback).
Or you can put out a facebook/freecycle message that you need carpet scraps. Even discontinued samples from a carpet store would work.
I'd still speak to her about getting reimbursed for spending your own money to protect her carpet from her workers.
