Mine came in as part of a wild caught shipment. Died before I could take her to the vet and find out what was wrong.
Completely agree with separating them. All 7 other frogs that came in with this frog died back to back.

A cricket keeper is fine as a quarantine tank. Use spring water and papertowles on the bottom. Add a glass feeder dish in the bottom of tank and put a large leaf like from a Peace Lilly in it. Change out the water & papertowels during the day when the frog sleeps. Watch for poop and keep a record of food intake and how often the frog poops.. this way if you do contact a vet about the frog they will have some history to look at as well as current condition.