Before you laughed at how she looked in her cervical collar you had plenty of kind, compassionate things you could have said and done that would have made her feelings for you, if anything, grow.
Now, you're fucked hard. The best you can do is immediately send an extremely extravagant bunch of flowers with an enormous apology note asking if there is anything she needs and telling her, repeatedly, how sorry you are for what happened and then wait for her to contact you. You really want to be smart, if she lives alone, offer to pay for maid and laundry service and have someone cook for her, that might encourage her to stay off her feet.