What is the going rate in the East Bay for splitting a nanny share or sitter?

Situation: I have a 2 year old daughter on several preschool waiting lists. My mother currently cares for my daughter but has told me she is done caring for children as of January 2019. 

I've researched nanny's and nanny shares and I have been unlucky in finding someone or family that fits my work schedule. And I feel at 2 years of age that my daughter could benefit a preschool environment. I work Mon-Thur 10 hour days and live in Walnut Creek near downtown. 

A friend of a friend has offered to care for my daughter while we wait to get into a preschool/daycare. She has a son close to my daughters age and lives in Lafayette, the direction of my commute. We had a play date and it seems like a good fit but we did not discuss money. I feel like we both were too shy to talk about money since we are very close to our mutual friend. 

Question: How much do I pay her per hour? Would it be a nanny share rate since she has her own son she is looking after? She doesn't have nanny experience but is a mom. 

On a side note she is currently pregnant with #2 and is due in April 2019. I'm nervous but she told me that she would let me know if she couldn't manage with taking care of my daughter.