Hello, I actually think you should speak to her only in Spanish. Most bilingual households have a rule of NO ENGLISH AT HOME because kids growing up in the US will always use English out of habit. She will learn English in school and will use the language with her classmates. Usually kids who are bilingual start out slowly with English or a second language because they lack vocabulary that monolingual kids have. However, I think over time the bilingual kids catch up and will be even! 

I wish my parents spoke to me in their native language more often and were adamant about it. I can speak it still but not so well...:(

In my experience, kids growing up in Spanish speaking homes don't learn to read in English very well UNLESS the parents  read to their kids in English as they are growing up.  It's the same thing for native English speaking families.  There are occasionally native English speaking kids who show up in Kindergarten who do not know how a book works- they do not know how to turn the pages- because their parents never read to them.  I would recommend that you read every day to your child in English AND in Spanish.  Begin by following your finger along the words as you read the book to your kid.  Ask your kid to point to things in the book as you read.  Ask questions like "Where is the butterfly?"  "Can you point to the butterfly?"

Your local library will probably have books in both Spanish and English for kids  Check out some kids' books in both languages and start reading to your kid right away.