Unless you get another school, no. Fish that school want fish of their species and type, they are much happier with their own type.
Two females shouldn't be housed together in a 20 gallon. You said you don't think you can save one, so if she is weaker she will most likely get bullied. When you rescue a fish please make you sure you have the proper setups and you know diseases and all that, cause then it could be as bad as in the petstore. If they are both ill you don't want them in the same water, one could have a nasty disease while the other could be fine, you put them together, they are both sick... Separate housing when doing rescues is a must.
15 Gallon NPT
1g no tech bowl in the making