Jennifer, it sounds to me as though you are already doing pretty much what you should be doing to encourage your daughter’s speech and language development. And I confidently predict that, by the time you read this answer, your daughter will be using more sounds and producing recognizable words.
Before offering specific suggestions, let me make my most important comment: you want to make certain that, in your concern for language progress, you don’t make her anxious about talking. If you correct her too often, or frequently ask her to repeat something she said, she may become so anxious about the process that she won’t try to talk at all.
Now for some specific suggestions. First of all, make certain that she hears adequately. Do an informal test on your own, such as calling her name when her back is turned and noticing whether she turns her head to you. If you have any questions about this, discuss it with your pediatrician who can do some tests and then refer you to a speech and language specialist if warranted.
In the meantime, by all means continue reading to her. Encourage her to point to (or touch) pictures of words you are certain she understands. Slow down your reading tempo just a bit and exaggerate certain sounds. From your comment it seems as though she doesn’t produce vowels. So when you read or talk to her, draw those sounds out a bit—not enough to sound artificial but just enough to highlight them. “SEEE the bAYbEEE in the snOHw.” “I sEEE a bIg trUHck.”
When she is facing you up close, make the consonant sounds that are clearly visible (start with “m,” “b,” and “p”) along with a vowel (“ma-ma,” “bay-bee,” “pa-pa”) and encourage her to imitate you. She may move her lips correctly but not produce the vowel sound. If she does that, praise her, anyway. Name her toys for her, again in the slightly exaggerated way. Sing with her, and to her, and encourage her to clap and “sing” with you. “Announce” your own actions when you are doing things with and for her. “Mommy’s going to get your lunch now. Do you want to wait in your high chair?” Her presumably more linguistically competent older brother may intimidate her. Even so, she will probably come into her own before long.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.