L.,
You have gotten great advice. All of our kiddos in my family suffered from stinky feet. The advice from our pediatrician as this: IT has been super effective in all 4 of them so far for over 20 years.
1. where cotton white socks as often as possible
2. never wear leather/tennis shoes without socks
3. DO NOT wear the same pair of shoes 2 days in a row
4. Have at least 2 pairs of shoes for her even if they look exactly the same.
5. as soon as warm enough wear sandals as much as possible ( again more that one pair , never 2 days in a row)
6. make sure shoes are properly fitted by a TRUE shoes specialist. ( I love Feet First for Kids at 81st and Harvard, there is also Trippets at 27th and Harvard)
The problem is most likely her feet perspire during the day. the shoes do not completely dry out , so fungus, mildew etc grow and accumulate. Her current shoes are most likely toast. Time to start over and see what happens.
the newspaper thing works great!!, Darling hubby has to wear socks even with sandals. ( I know totally scandalous) but if he doesn't they will smell so bad you can smell him coming.
Don't let her sleep in socks/footed pajamas so she has time to dry out in the evening. let her go barefoot when at home.
Podiatrist will tell you barefoot is best anyway
good luck let us know what works