She could possibly register the item as a 'registered design' under UK IP law, but it is doubtful that she would meet the criteria. The design idea must be new, which probably doesn't apply to printing babies handprints onto pieces of glass.
Is the other printer seriously claiming to be the first person to print a babies hand print onto glass or any other sublimation product? I have just done a quick google search and come up with half a dozen UK companies offering printed glass tiles and other objects with hand and footprints. There are thousands of people offering sublimation products in th UK - many of those will have done something involving handprints.
She is offering nothing new.
Another "twist to the plot" ...
Most of the Copyright and Patent laws are now somewhat "harmonized" between the US and the UK, mainly through international treaty, however the "twist" here to be considered is the issue of privacy rights
In the US the privacy rights are not under US Federal jurisdiction but rather bound by State by State laws. But more or less the States have similar laws regarding privacy rights.
Case in point; If I take a photo of someone I own the copyright to that specific
image, but I may not be able to benefit financially or be able to share or publish that photo.
For this reason when using models for product advertising we use a "Model Release Form" where the person being photographed would sign a release form allowing use of their image, even though technically the person who took the picture has a legitimate claim to copyright. Just the copyright cannot be "exploited" and really can only be used for ones own "personal consumption" unless the person in the picture allows it.
But of course in the case of a photo unless that person was a celebrity then there really isn't any commercial value except to the party wanting the photo. But a baby footprint since it is unique to the baby, then that baby (actually the parents) has privacy rights along with the person creating the art has a copyright. Of course a copyright that can't really be "exploited".
So the person taking the picture and creating art from it should still be able to claim a copyright as the the footprint is unique. Of course the footprint came from someone that is allowing you to use it to create a product, no different than if someone wanted their babies picture on a tshirt to give to Grandma.
In this case the idea or concept is not able to be copyright, nor patentable, but certainly the image as it is unique could have copyright.
So I would throw out there that the specific
"art" is subject to copyright (but can't be exploited), the subject of the art has privacy rights, and the concept
of this generically can neither be copyrighted nor patented.
Just FYI on privacy rights here in the US ...
Privacy and Publicity Rights
In the US we have what we call "design patents" which are not "utility" patents that encompass functional inventions. But these are not intended for "flat" art like a photo but rather a product shape or sculpture. These are typically designs that are in 3 dimensions, for example an iPhone case which isn't flat. The term "ornamentality" is used and really means is has 3 dimensional elements in it and the entirety is not a flat surface.
So I think at least in the US you couldn't get a "design patent" for a hand or fingerprint, unless it was cast in plaster or something. I suspect that a 'registered design' in the UK is something similar.