Should I dump this girl?

we've been going out for like a month and we went to an amusement park, we had to go with her 11 year old sister which sucked to begin with. but then, her little sister was walking without her sandals on, and cut her foot...so my lovely girlfriend asked me to carry her, so i was like ugh fine. at first she rode on my back, but she kept sliding off, so my girlfriend was like "why don't you put her up on your shoulders" i was like are you serious? and she was like yea why not? so basically the whole day i had to walk around with her bratty little sister sitting on my shoulders in a tshirt and a bathing suit bottom...and neither of them were at all thankful...should i dump this girl?