Her baptism crtificate has:

Bapt date:     18 Oct 1899
Name:          Eleanor Mona Powys
Parents:       Robert Vernon and Wihlemina Powys
Abode:         Cathcarl    [actually Cathcart, Cape of Good Hope, South Africa]
Birth date:    29 March 1899
_____________________

Her baptism with birth date was on the same image as that for Nesta Isabella Hart Powys and provided by Ancestry, as well as Family Search.  Transcript by me for the joint entry:

>              Cape of Good Hope  >  Cathcart  >  Baptisms 1880-1969

“BAPTISMS solemnised in the Wesleyan-Methodist Chapel . . . .
“   in the County of  . . . . .  in the Year of 1899
“. . . .
“When Baptised:       October 18th. 1899
“No:                  660
“Parents’ Forenames:  Robert Vernon and Wihlemina
“Parents’ Surname:    Powys
“Abode:               Cathcarl  or, on other pages, Cathcart
Celebrant:            Geo H.P.Jacques

                      First child            Second child
                      ===========            ============
“Child’s Forename:    Nesta Isabella Hart    Eleanor Mona
“When born:           May 16th 1895          March 29th 1899
________________________