My daughter was 17 for 6 months of 2017 and 18 for the balance. Do I claim her as a dependant?

So long as there are credits that you can claim on her as a dependent (ex: tuition transfer, disability transfer, etc…), you can still add her no matter how old she is.

Here are some frequently asked questions about dependants: https://turbotax.community.intuit.ca/replies/3351149