"How did Brenda get involved when she was signed to Motown?"
A good question. It would depend on the wording of her contract with the company, though that didn't stop the Detroit Motown session musicians from doing a lot of moonlighting. As these recordings were done in Los Angeles they were probably well out of the reach of Mr Gordy's extensive Contract-Police spy network!!
The Wooden Nickels "Nobody But You" has appeared on a couple of Kent's NS compilations.
Brenda is also believed to have been one of The Belles who recorded "Let's Pretend" for Mirwood in 1966.
https://www.45cat.com/record/5505Roger