If she is using the camera for web based photos in controlled light situations (Ie. window light, exactly what she's using) then she does NOT need a DSLR, and solely using a DSLR will NOT give 'infinitely better results' over a compact camera.
The only benefit that a DSLR would have over a decent compact camera on image quality in her situation would be a reduced depth of field, which would have a limited-to-negligible impact on overall image quality. Even then, using a large aperture compact camera appropriately could yield matching DOF capabilities.
Knowing how to use light and composition will have a much greater impact on her photos. If she/you pokes around photo blogs and sites for a while, you would have no trouble finding a straightforward guide to using natural light correctly to light food/still life. The camera is a tiny part of the image quality equation in this particular situation. Check out fstoppers.com, or even ehow.com or something along that line.
I would recommend she gets one of the upper level compact cameras, which would remain small and simple, while still having very usable large apertures and dynamic range. The Canon s90 is a very very good camera considering it's size and price, and can be found for under $200 used according to amazon. She could also check into buying a refurbished one from BH photo, which probably comes with a warranty/guarantee.
The specific camera model isn't particularly important, more so look for cameras that are recommended for solid technical functions over chintzy features. Any of the upper level Nikon/Canon lines will have something suitable, and I'm sure other brands probably do too.