I wouldn't pay more than about $150 for that machine, and that's only because of the seven drawer cabinet (which are quite desirable). The machine is quite a common Singer model 27 and the Sphinx decals are quite shabby. Model 27s are vibrating shuttle machines, and although they make quite a good stitch (and will stitch through just about anything) you could get a model 15 in the same cabinet and with the same decals for about the same price. With a 15, you'd be much better off for quilting, embroidering and obtaining spares parts (model 15 bobbins are the most common type available in the world) and they will also stitch through just about anything.
If it were me, I'd offer $100 for the cabinet and put a 15-91 or 201 in it (get one of each, the heads usually go for almost nothing). They are machines you would be truly happy to treadle.
Sorry to be the bearer of bad news for her but the machine head is only worth about $20 (at least here).