Amy,
I"m not sure from your post. She is footsore now, correct? Is she confined to a stall 24/7? What is STP?  I'm just clarifying these questions for either Dr. Kellon or one of the mods with experience with metformin who can help you. 
--
Dawn Wagstaff and Tipperary   

Saline, MI  2003

Tipperary Case History

Juniper Case history: https://ecir.groups.io/g/CaseHistory/files/Dawn%20and%20Juniper/Case%20history%20Juniper.pdf .