If its footcare, as in providing medical treatment, she's fine.
https://www.gov.uk/guidance/national-lockdown-stay-at-home#sports-and-physical-activity
If its footcare as in cosmetic stuff, she can't.
I do have a little sympathy with the government, as much as it pains me to do so. This is an emergency response, not something that's been many years in the planning. As comprehensive as they try to be there's always someone slightly different in some manner who wonders if they're exempt in some way. "Podiatry is banned, but I'm a one legged podiatrist who practices from a bus shelter and im not listed." Well, in instances like that it seems simple to me - if it isn't in black and white on the gov.uk website telling you that you can do it, then you can't.