One guppy left!!? i really am not sure what to do any suggestions?

i gave all mt guppies away... well at least i thought i did but then i realized there was onlt one baby left in my 2.5 gallon aquarium anyway idk what to do with it ??.. should i add more fish if i should what kind?.. noot to big it is a 2.5 gallon i don't want any more guppies i was really hopeing to get a female betta but if it is a male guppy and colour ful it will kill it could this work a guppy and a female betta?