Need I find a companion for my single ADF?

They can live fine in groups or by themselves - they can be in any mix of genders so all females would be just fine.

But, before you add any frogs to this tank, do you know why your male died? Also, all new frogs need to be quarantined for 30 days or you risk them infecting your current female and her dying also.

Thank you! Now I prefer to let her live alone, after all adding new one may be risky. My dead male ADF performed normally and ate two living bloodworms actively the day before he died. I did not find anything abnormal on his body. His abdomen was just thin all the time since I bought him three months ago. I am very very sad on his death......However, the female behaviors well now.