Hi I think if you think there is something noticeably wrong with one side as compared to another than I suggest show it took her pediatrician. Else it may be that some mosquito may have bitten her because of which the swelling is there as the babies skin is very tender and can get swelled because of an insect bite. See for a day or two and if it doesn't subside show it to her doctor.
Sabina Khatun