I haven't signed anything over, at least I don't think so.Have you signed over the rights or the usage of the design?
If not, then you still retain them even if she's paid you 50%.
Say if you agreed to design a logo for a client for say £400 and you get paid and the client gets a new logo.
Unless you sign over the full rights then technically, you still own it and you could ask for additional payment every time they use it for something different "usage".
Thanks for clearing that up