i have 2 possibility.
First she is Shiraoki-sama. Matikanefukukitaru strongly believe in fortune. she love fortune-telling, always carry lucky charm. and she pray upon Shiraoki-sama, her irl ancestor, for blessing.
Second is her "Twin". Horse usually pregnant a foal, but if racing horse have a twin, breeder often get rid off one of them. because twin foal will fight for nutrients and sometime grow too weak for racing.