You need to tell her yourself.
I see in your other question you said you plan to keep and raise the baby, and were asking for advice on how to earn money.
You are 14. Pregnant or not, at 14 you CANNOT get a job that is going to pay anywhere near enough to support a baby. (And, unless you expect your boyfriend to drop out of high school and spend the next 50 years doing unskilled work, HE can't either.) Legally, you have to go to school. In most states 14 year olds can't work at all, or are VERY limited in the type of job and the hours they can work.
If you have the baby, your PARENTS will be raising it, caring for it, and suporting it while YOU finish school. Are you fine with ruining THEIR lives as well as your own?
You are clearly NOT mature enough to raise a child, since if you WERE mature enough, you would have not been having sex at all -- or would have used birth control. (Maturity means the ability to think about consequences -- not just take off your pants.)
So yeah -- you'll need to just tell your parents. And if you do plan to keep the baby, be sure that THEY are fine with giving up THEIR lives and jobs for the next 5-10 years, to deal with your poor decision-making.