Well, lemon juice is given to dilute some poisons in the system, but it will probably make her sick to her stomach and possibly make her vomit. You need to get her some water tol dilute the lemon juice and watch to make sure she doesn't act out of sorts. If that happens, please call your vet. She may be having a mild reaction to the amount of juice she drank undiluted.
Please let me know if I can help further.