crossing border into Canada with Washington drivers license

I believe you need proof of citizenship, which can be a passport, an Enhanced WA DL or a regular WA DL and birth certificate.

All Washington state DL's are EDLs now. The license will tell you btw. Should have zero issue in or out.

A Enhanced drivers license is sufficient. The trick is you can only get an enhanced drivers license if you can prove citizenship. There is a list of acceptable documents on this website.
https://dol.wa.gov/driver-licenses-and-permits/enhanced-driver-license-edl

Not all Washington Licenses are enhanced. The information posted previously does not match with current info on DOL website.

What does her Washington license look like?

Enhanced-- https://dol.wa.gov/media/84/download?inline

OR

"Regular"---https://dol.wa.gov/media/77/download?inline

Canada entry requirements:

US travellers
What you need to bring to Canada as an American depends on whether you’re a citizen or a permanent resident.
American citizens
In most cases, you must travel with your valid US passport.
If you don’t have a valid passport, there are other documents you can show. These include, but are not limited to your
birth certificate
certificate of citizenship or naturalization
certificate of Indian status, along with photo identification
US enhanced driver’s license
https://www.canada.ca/en/immigration-refugees-citizenship/services/visit-canada/entry-requirements-country.html#american-traveller

EDLs are acceptable for entry into the U.S. from Canada, Mexico, Bermuda, and the Caribbean at any land or sea port of entry – not just at ports of entry in the issuing states or provinces.
https://www.cbp.gov/travel/us-citizens/western-hemisphere-travel-initiative/faqs#
https://dol.wa.gov/driver-licenses-and-permits/enhanced-driver-license-edl/guide-enhanced-driver-licenses-edl

My WA DL is not an Enhanced DL.

Assuming you mean a land crossing, if so, a passport card works.

@ Jules. If she doesn’t have a passport, she won’t have a passport card……..

@ Carol now retired, that is not true. I know a few people that have little interest in international travel that do travel to Canada and have passport cards. https://travel.state.gov/content/travel/en/passports/need-passport/card.html Additionally, this past Friday, I took my mother to obtain a passport and she was specifically asked if she wanted a book or card or both.

ah, point taken. all REAL ID compliant DLs in Washington State are EDLs.