Origin

Gin is made from grain and juniper berries, the fruit is still plentiful and picked in London even today. I know of people who gather these wild fruits in order to make their own home-made gin, the recipe is very simple. The word gin is derived from genièvre (French), genever or jenever (Dutch), and ginepro (Italian) all meaning juniper.

Why is it called mother's ruin? Well, as mentioned by the OP it was a cheap means for forgetting your worries. And as we all know, alcohol is by nature addictive, and whereas today's gin is about 40% ABV (alcohol by volume), it was likely the homemade distilled concoction to be much greater, possibly as much as 50%. Thus a cheap, widely available, legal and highly-intoxicating spirit that proved to be an irresistible and lethal combination. It was a time when alcohol was safer to drink than mains water and, because gin wasn’t taxed, it was even cheaper than beer. It was the 18th century crack of the poor.

Until I did some research, I had always believed the myth that gin was a depressant. An English male friend once told me that gin did not make you feel merry, nor lead you to experience that feeling of euphoria which other spirits do. He explained that was why women who were in the habit of drinking gin were more likely to become depressed. I believed it, it sounded plausible until today that is.

Gin Doesn't Make You Sad

Few spirits bear so heavy a semiotic burden as gin, which is regarded by many as mother’s ruin, the destroyer, the devil, the drink that shall not be named. [...] This bad rap, I think, is partly the fault of the English artist William Hogarth. The gin of 18th-century England — harsh and cheap — is very different from what we drink now, but anyone who was shown a slide of Hogarth’s “Gin Lane” in history class is unlikely to forget the images of those dissolute Londoners: here, a man fighting a dog for a bone; there, a woman dropping her baby over a railing. There was a time when I, too, bought into the cautionary folklore. I spent much of a particularly hot, sticky New York summer drinking nothing but gin and tonic, an order that seemed to me sophisticated enough for a young woman trying her best to feel like an adult. As the weeks wore on, though, I was having a bad time of it. Relationships weren’t working out. Work was a slog. I was down. Ascribing to it powerful depressant qualities, I blamed the gin. I gave it up. For years. When I finally came back around, I approached gin with caution. Nothing happened. I felt just fine. More than fine. I came to love the stuff more than ever. And I realized it wasn’t the gin that had bummed me out all those years earlier; it was life.

It has been argued that the epithet, Mother's ruin, is largely to be blamed on William Hogarth's famous engravings; Beer Street and Gin Lane where a young mother, half-naked, inebriated, is more concerned with the object she has in hand (a snuff box?) than her baby's safety. The link above suggests that a woman called Judith Dufour is thought to be the source of Hogarth's inspiration; in 1734 she had collected her two-year-old daughter from the workhouse only to later strangle the infant, strip her naked, and leave the body in a street ditch in order to sell her new clothes for gin money. The mother was later convicted and hanged for her heinous crime. In another infamous case, Mary Estwick slept in a gin-induced stupor while yet another small child burned to death.

Such cases provided a focus for anti-gin campaigners such as the indefatigable Thomas Wilson and the image of the neglectful mother became increasingly central to anti-gin propaganda

One source claims that for every five lower-class children born in London during the 1720s and 30s, four died before the age of five.

Distilling Gin Myths

Indeed, most attribute the ‘Mother’s Ruin’ label to artist William Hogarth, who in 1751 published a series of etchings, including one called ‘Gin Lane’ that depicted disturbing scenes of a gin-soaked London. Desolate buildings and squalor dominate the picture, in which the only thriving business is the funeral home. Another etching, ‘Beer Street’, shows an affluent, thriving London. The contrast – and meaning – is clear

Beerhouse Act 1830

Why the term, "mother's ruin" made its appearance in the 1820s

In 1830 the Duke of Wellington's administration passed the Sale of Beer Act, which removed all taxes on beer, and permitted anyone to open a Beer Shop on payment of a two-guinea fee. This Bill along with rising cost of grain helped virtually end the traffic in gin smuggling.

As a result of the Gin Act passed in 1751, which had been designed to control the consumption of gin, spirit retailers still required licences to sell from rented premises at the cost of £10 a year. In order to compete with the increasingly popular beer shops, licensees devised the 'gin palaces' which first appeared about 1830. Gin palaces were large, imposing and handsome and even luxuriously furnished. By the 1850s there were about 5,000 such places in London.

Gin Craze

there was a resurgence of gin consumption during the Victorian era, with numerous 'Gin Palaces' appearing.

It was only in the second half of the 19th century that gin became associated as mother's ruin. Until then it had been known as Dutch courage, Madam Geneva, Mother's milk, (perhaps inspired by Hogarth's print in 1751?) Mrs Gin as seen in the pamphlet entitled "The Downfall of Mrs Gin" depicted in Hogarth's engraving, and finally blue ruin. Eric Partridge in his A Dictionary of Slang and Unconventional English confirms the dates.