mother (honorific); wet nurse (honorific)
Dated honorific term for one's own or someone else's mother, or for a wet nurse. In modern Japanese, お母さん or 母上 are more common for 'mother', and 乳母 is used for 'wet nurse'.
In old documents, 'みおも' was used as a respectful term for one's mother.
In this tale, the wet nurse (みおも) takes care of the young princess.
The common modern term for 'wet nurse'. みおも can also mean 'wet nurse' but is archaic.
The reading みおも is likely composed of the honorific prefix 御 (み) and 母 (おも), an old word for 'mother'. The exact derivation is uncertain, but it is an archaic honorific term.