My 6 Month Old Daughter's Feet Are Swollen , After

My 6 month old daughter's feet are swollen , after a day at the aquarium, wasn't sure what the cause was being that I had her in a carrier for majority of the time, and there are appears to be what looks like a red rash/bite mark only on one foot but not the other and both feet are swollen so I feel like It may not be due too the rash/bite mark... ? I'm thinking that I need to just take her to the emergency room because the swelling has yet to go down, but she is acting like her usual self... what do you think may be the cause or what I should do ?