Not a lot is known about Screwloose's background. She doesn't think about it an awful lot and doesn't really have the means to talk about it to anypony else, at least coherently. Perhaps if she were to be questioned by one who understood dogspeak she might be able to fill in the gaps for us.

What we do know is that she at some point she assisted a nursepony in returning Rainbow Dash by telling her to wait in her own way (BARK BARK BARK! roughly translates as "Wait Rainbow Dash! Wait!" for those not quite versed in dog))