There is a $50 upgrade for Silhouette Studio to import SVG's.
This post is a little long but I hope lots of info. Converting files can be confusing.
You can cut from Inkscape to the Silhouette. You can bypass all of that confusing converting files. Here's a Inkscape/Silhouette forum: Inkscape Cutting Design • Index page
I do not have a Cameo but I was a long time Silhouette/Wishblade user. I used to cut from Inkscape all the time. I actually preferred it.
You can not convert SVG-GSD. GSD is a proprietary format only licensed by Graphtec. You can convert SVG-DXF. Silhouette Studio can open DXF. Just save your file in DXF format from Inkscape. Go to Silhouette Studio and import/open the DXF file.
There are two important things to remember about this conversion.
First DXF has some problems. Either the conversion goes awry and your missing pieces. The file is huge and needs to be resized. When I say huge I mean by 1000%. There are a few other headaches too. Then sometimes you can get perfect files.
Also when you convert a SVG or any vector image to another format your degrading the quality of that image. Your file will now have extra nodes, less nodes or even missing pieces. A lot of times this will not be noticeable. Once this file starts cutting in your machine it can put extra wear and tear on your machine. This will cause damage in the long run.
Converting SVG to PNG. The reason your DD could not cut from PNG is because the file was converted to an Image file. You need a Vector file. The file has to be traced again.
The best way to convert a file is through a virtual printer like doPDF or CutePDF. Both programs are freeware. You use these programs just like a printer. Instead of printing you will have a PDF file instead. You can open this file in your software. If I remember correctly Silhouette Studio does not have PDF import. They might have added it in a recent update. I don't know for sure.
When you virtual print your PDF file the PDF is saved in the original format. For example you save in a vector program the file will open as a vector. You save as JPEG the file will open in another program as a JPEG. That's why SCAL & MTC both have PDF import for their files. That's why those programs lock up when importing some PDF's because people are trying to import a PDF file that was saved in a Graphic program that handles JPEG's. If you "print" PDF from Inkscape, for example, open PDF in MTC it opens perfectly because both those programs are vector base. I hope that was not confusing.
I know a lot of the things I posted are probably confusing. I hope I explained it a bit better and can help your DD with her new X-mas gift.