There is very little firm evidence that rural women wore different clothes following their marriage, the birth of a child or the death of a husband. If such customs existed they may have been different from place to place and time to time.

The Cap
There are a few indications that rural women in Wales wore caps which completely covered their hair after marriage. Almost no illustrations of Welsh rural women show any hair except those of a few young women, including Jenny Jones. A similar custom may have been followed in other countries.

’Stafell or Ystafell (Trousseau)
There are a very few indications that women gathered clothes and domestic items before marriage.

Marriage gifts
A very few references suggest that a husband or mother made a gift of clothes to a bride.

Cowyll:  A garment, or cloke with a veil, presented by the husband to his bride on the morning after marriage ; and in a wider sense, the settlement he made on her of goods and chattels, adequate to her rank.
Pughe, William Owen, A dictionary of the Welsh language (1832) [based on the early mediaeval Welsh laws]

The young women wear on the head only a narrow ribbon to tie the hair, and a cap; but in some parts, immediately after marriage, a handkerchief is added. This is made into a triangle by being doubled, is thrown over the head, folded under the chin, and the long ends tied into a knot at the back of the neck.
The Rev John Blackwell, (Alun, 1797-1840), curate of Holywell and Rector of Manordeifi (Pembrokeshire),  ‘On the Advantages Resulting from the Preservation of the Welsh Language and the National Costumes of Wales.’
The Welsh version was published anonymously under the title ‘Gwisgaid y Cymru in Cylchgrawn y Gymdeithas er Taenu Gwybodaeth Fuddiol am 1834, dan olygiad y Parch John Blackwell, B.A., (Llanymddyfri, gan D.R. and W. Rees, 1834), pp. 274-276
This was published in English, as a translation from the Welsh in Beauties of Alun; being the Literary Remains, in Welsh and English, of the late The Rev John Blackwell, B.A., (Ruthin and London, 1851), edited by G. Edwards (Gutyn Padarn), pp. 253-266 which states that ‘This essay was intended for the Cardiff Eisteddfod, [1834] but sent in too late for the adjudication.’
The English translation was also published in The Cambrian Journal, (Cambrian Institute), Tenby, 1861, pp. 26-38, in which it was prefaced by the following: ‘We reprint the following essay by the late eminent Bard and Scholar, Blackwell ; especially as it furnishes valuable information on a subject that is engaging a good deal of the public attention just now, that is, the National Costume of the Welsh.
Its publication in 1861 may have been a response to questions about Welsh costume published in the Cambrian Journal for 1858, pp. 366-367 (see below).

’STAFELL, or Ystafell, is also used for the store of clothes, household furniture, &c., which the Bride collects before the day of marriage, and makes a display of at the time.”—Richards’s Welsh Dictionary.
I have always noticed with approbation the provident care which the young Welsh females take to lay in a little store of useful articles, such as household furniture, abundance of substantial garments, and other things necessary to begin the domestic arrangements with comfort, previous to their marriage. In fact, the collection is begun almost from infancy, and is continued until they meet with “a man to their mind.” These, generally, consist of homespun blankets, feather beds, crockery, and dairy or kitchen requisites; and so far from considering this care as an indication of a precocious expectation or intention of wedlock, I feel confident, it is rather an assurance that it will not, generally speaking, be entered into unadvisedly. It might, perhaps, be desirable that their English, and more especially their Irish neighbours, imitated them in this point at least.
Bowen, Melesina, Ystradffin : a descriptive poem, with an appendix, containing historical and explanatory notes(London, Llandovery : 1839), p. 175

Her great care, however, was the staffell. A staffell, be it known, is the trousseau of the lower classes in Wales, but it embraces a greater number of articles than that fashionable appendage to a lady’s bridal. The generosity and attachment of the man does not, generally speaking, make him unmindful of his household comforts, which he expects his intended wife to provide for him, before he takes her “for better for worse.” Your accomplished and elegant lover looks for his ten or twenty thousand pounds as an indemnification for the disagreeables he imposes upon himself in matrimony, whilst your Welsh rustic swain expects bed and bedding, chairs and tables, cups and saucers, and the like, to repay him for the difficulties he entails upon himself. The earliest and most earnest desire of a Welshwoman is, therefore, to procure a good staffell.
We will take Sally as an instance of this. She entered service when she was about sixteen—she is now nearly thirty. What did she purchase with the first five shillings she received? Two cups with red and yellow birds upon them, a jug, a pictured plate, and a tea-cup and saucer. It is true that she sadly wanted a new gown, and that she was obliged to go without stockings, Sundays excepted …  She has teacups and saucers without end…  all these she has, and much more, which has absorbed her income, or a considerable part of it, from the age of sixteen to thirty. I must be understood to cast no aspersions on her Sunday attire, which is always smart enough, and her boxes are quite as much swelled with best clothes, as her mother’s shelves with crockery-ware; but honesty obliges me to confess that her every-day garb is not the most attractive. …
During the first six months of her second year at Grongar, Rachel did not give her attention to her staffell with any degree of laudable care. The multiplicity of gowns, petticoats, caps, aprons, handkerchiefs, and hats which usually crowd the drawers and boxes of the betrothed, had not yet entered hers. Another winter and summer passed before she thought it necessary to make any purchases. When autumn began, however, her wardrobe increased by degrees, and occasional articles of the dearly loved earthenware also swelled her stores. …  Any one who looked at Sally’s untidy figure, cased in a very coarse pinafore, which served for gown, apron, and neckerchief, need not be particularly astonished at the wavering dispositions of her lovers;
Beale, Anne (1816-1900), The Vale of the Towey ; or Sketches in South Wales (1844), pp. 109, 616, republished as Traits and Stories of the Welsh Peasantry (1849); repeated in Goodrich, Samuel Griswold, Manners and Customs of the Principal Nations of the Globe, (Boston: 1845), p. 88-91 (and subsequent editions), pp. 91-92

Mrs Roberts of Mun-y-Nant, Llangollen told J R Jones in 1925 that the cloak ‘was always a mother’s present to her daughter when she got married.’
JR Jones Collection, NLW, vol. 2, p. 32