My friend lives in town and has horrible dandylions. I know it works well in the pastures on them but all I'm using is a 5 gal backpack sprayer and wondering what i should mix the rate as .....for roundup in it i think is like 1/2 to 1cup per gallon of water, i know this is strong but i want it dead. I do not want to kill her lawn for her so figured I'd ask for some help beforehand

thanks in advance