Jo Anna
I don’t think there is a definitive answer, but there is a good sequence to follow. Generally it is advised that one should get a new passport if it expires within 6 months of your travel date. You ‘may’ be refused entry by the country you are traveling to and returned on the next available flight. Knowing this, airlines (as a general practice) will often refuse to allow you to check in and fly, because they are obligated to return you to your country if you are refused entry. I am sure it is not a pleasant experience to be held by officials (guards) until put back on a plane.

If your grand daughter is in Canada, she should go to a Canadian Passport Office or Service Canada Office (that handles passports) and submit a completed passport (10 year) renewal application. She can download the form at:

https://www.canada.ca/content/dam/ircc/migration/ircc/english/passport/forms/pdf/pptc054.pdf

and actually fill most of it out online, using her old passport information as a guide, before printing it. She will need two copies of a recent passport photo to attach. Many locations to get same day photo with photographer stamp and date on back. No guarantor of photo is required, but she will need to write in the names and contact info from two individuals (non relatives) who have known her for some years (ask them first!). It is very clear on the form what needs to be done. Travel date has to be completed in appropriate section. If she has her airline ticket,(even electronic) take it in as well to show agent if requsting the urgent delivery option. Old passport has to be attached, but one can select it to be returned after it has been invalidated. It is delivered separately.

She needs to actually go to a Canada Passport Office or Service Canada Office that deals with Passports. She can make an appointment or just walk in and wait her turn. Some offices are much busier than others. Look online for closest one. If nearby walk in and talk to receptionist. Often easier than trying to book appointment online.
Agent will go over all application details with her to make sure it has been filled out properly. For an extra fee she can get one of two urgent services where she can pick up passport next day or within 10 days from that office.
Otherwise, passport applications currently submitted in person are processed within 10 days and mailed back by priority post. There is time but really she needs to do it all in person for certainty. She likely will want to schedule a pickup at the office. She can look up the fee online.

I did this process several months ago by going into Service Canada without an appointment. They checked my forms for completeness and I was out within an hour. I paid using a credit card while there. My old passport was returned within 10 days and my new passport arrived 2 days later.