Suggest Remedy For Swelling And Tenderness In Skin Due To Insect Bite

My daughter 10 years old, got an insect bite yesterday at the park. I did not see it but my brother did. He said it was a mosquito and he caught saw the drops of blood on her leg. Later, she had some pain in her leg and by nighttime she had a rash on her torso. I applied calamine lotion to it and it seems to have disappeared. The area of the insect bite is red, and swollen. It is tender to touch and feels hot. Should I take her to the ER?