5-FU can cause Hand-Foot Syndrome, even when taken as a once-every-2 weeks infusion; taking it continuously is pretty much like taking Xeloda pills twicee daily.
BUT, HFS is caused by the drug leaking from very fine capllaries in the palsms and soles, and eventually killing the cells on those surfaces; and 'swelling' (I presume of the whole foot, possibly ankles, too) is NOT among the HFS symptoms.
Nor is swelling/blisters; see:
http://www.chemocare.com/managing/handfoot_syndrome.aspThe fact that her toes are involved *might* be caused by that leaking drug being trapped in her shoes, I dunno.
In any case, she is certainly at risk of HFS as a patient receiving continuous 5FU, and she should follow all the precautions mentioned in that link.
Especially to limit the amount of walking.
Also, wearing socks significantly reduces the friction on the sole of the foot and on toes.
And if the pavement she walks on has gotten hot with the spring sunshine, that would further aggravate the condition.
This might just be 'normal' foot problems aggravated by the drugs and extensive walking, rather than true HFS.
Or she may have new shoes that don't fit properly, or is wearing them without socks or hose.
Depending on the extent of her autism and awareness of her world, she might even be walking around barefoot now that it's warmer.
Calling the oncall doc is certainly a good idea; staying off her feet would probably the number one recommendation, possibly along with Tylenol for pain relief.