Miss Mary Hanwell was born in Kidlington in 1790/1, the daughter of John & Hannah Hanwell, and was baptised there on 26 January 1791. She ran a boarding school for young ladies in Kidlington until 1822.

In that year she moved her school to St Andrew's Road (then Church Street) in Old Headington, and the following announcement appeared in Jackson's Oxford Journal on 12 October 1822:

LADIES' SEMINARY, AT HEADINGTON, near OXFORD.
MISS HANWELL respectfully informs her friends and the public, she has removed her SCHOOL from Kidlington to a more commodious house at Headington, where every attention will be paid to the health, morals, and improvement of her Pupils.
TERMS: Under 10 years of age £14 14 0; Above 10 £16 16 0
French, Music, &c. &c. on moderate terms
Day Scholars, Half a Guinea per Quarter.

The school, which was known as “Miss Hanwell’s Seminary”, was described as being near St Andrew's Church, and was run in a large detached house.

Every January and July Miss Hanwell advertised the start of her school terms in Jackson's Oxford Journal, and the school is listed in Pigot’s Directory for 1830.

On 25 July 1840 the case of Hanwell v. Parsons was reported in Jackson's Oxford Journal. Mary Hanwell brought an action to recover from the defendant, Mr Parsons (a farmer of Waterstock) the sum of £8 8s. due to her as a consequence of his removing his two daughters from the her school without giving a quarter's notice, as required by her prospectus. Charlotte Nalder, who had been a teacher at the school for nine years, remembered the defendant having three daughters there, with the last two being removed at Christmas 1834. William Baxter said that he had been printing the cards with the same conditions for the school for thirty years. On hearing that the girls were to be removed to Miss Wells's school, one of the daughters, Jane Parsons, reported that “Miss Hanwell said that Miss Wells's was a poor proud stuck up school.” Miss Hanwell won her case.

At the time of the 1841 census Miss Hanwell’s Seminary had sixteen girl pupil boarders aged between 9 and 15.

The Headington ratebook for 1850 shows that Miss Hanwell owned as well as occupied the school building in St Andrew's Road, and that its rateable value was then £24 and its gross estimated rental £30.

At the time of the 1851 census there were only five girls, aged from 11 to 13, at the school

In 1861 Miss Hanwell (70) was still living at the school; the teacher was Miss Sarah Manning (16); and there were just three pupils boarding there.

The 1861 census shows Miss Mary Hanwell (70) living in her school in St Andrew's Road with a 16-year-old teacher called Sarah Manning and just three girl boarders.

On 18 January 1862 the following notice appeared in Jackson’s Oxford Journal:

DIED. Jan. 15, at her residence, Ladies’ Seminary, Headington, near Oxford, Miss Hanwell, age 71.

She was buried at Kidlington five days later. Her effects came to under £300, and her executor was her sister, Miss Hannah Hanwell of Kidlington.

The school closed immediately after Miss Hanwell’s death. On 15 March 1862 Jackson's Oxford Journal announced as follows the forthcoming auction at the Roebuck Hotel in Oxford:

A DETACHED FAMILY RESIDENCE,
GARDEN and PLEASURE GROUND,
COACH-HOUSE and STABLE,
NEAR THE CHURCH,
In the centre of the Village of HEADINGTON,
(Freehold and free of Land-Tax,)
TO BE SOLD BY AUCTION by Mr. R. PIKE,
At the Roebuck Hotel, Oxford, on Saturday the 29th of March 1862, at Three o'clock (under conditions then to be produced),—A detached FAMILY RESIDENCE, for many years occupied by the late owner as a Ladies' School, containing entrance hall, drawing room 17 x 18; dining room, 17 x 18; breakfast room, and library, seven bed rooms, kitchen, scullery, larder, cellar, and other conveniences; also coach-house and stable attached, a large garden and pleasure-ground, planted with numerous choice fruit trees, in full bearing, having a side entrance thereto from the street, the whole occupying a considerable site, and in the most desirable part of this very healthy village....

A separate notice announced an auction of the contents of her house to be held on the premises on 25 March:

Mahogany four-post, tent, and other bedsteads, with damask, chintz, and dimity hangings; capital feather beds, mattresses, and bedding; mahogany and painted chests of drawers, dressing tables and glasses, wash stands, toilet services, and other the usual chamber appendages for seven bed rooms; sets of mahogany and maple dining, loo, and other tables; sofas, couches, lounging chairs, chiffonnières, carpets, rugs, damask and moreen window curtains; two square pianofortes, music stools, Canterbury, school mas, book shelves, and kitchen requisites; also a double-bodied phaeton, with patent axles and elliptic springs; pair of new gig lamps, garden tools, and other effects.