M.K.
I come from a loooong line of ingrown tonail'ers. Before bedtime, have her sit on the counter and put her feet in the (newly cleanly scrubbed) kitchen sink. Run the water as warm as it can be without burning and put some epsom salts in it. Have her soak her feet and 'give' her a mini pedi/foot massage. Give her a special treat to keep her occupied and while your down there, get a good luck at the toe. Make sure there isn't a puss bubble. If there is, gently hold the skin away from the toenail and gently push to release the pus until it's gone (gross, I know). Soak a little longer and then rub in a little polysporin. Let her go to bed and then repeat until the nail grows out or the infection is gone.
I just had to do this with my 15 month old. He's such a squirmer!! And it works for the occasional fingernail, too.