Civil Registration Indexes (Births)
Probably:

Mabel Howitt, reg. 1st quarter of 1877, Southampton, Hampshire, England.
Mabel Howitt, reg. 2nd quarter of 1878, Marylebone, London, England.
Mabel Howitt, reg. 2nd quarter of 1879, Northampton, Northamptonshire, England.
Mabel Howitt, reg. 4th quarter of 1880, Newark, Nottinghamshire, England.
Mabel Mary Howitt, reg. 4th quarter of 1880, Grantham, Lincolnshire, England.
Mabel Annie Howitt, reg. 1st quarter of 1887, Norwich, Norfolk, England.