So, the industrialization of fabric making made fabric super cheap which opened the door to a woman being able to have an absolute bonanza of clothing if she wanted it/could afford it. I don't know what you mean by ordinary in this context, but a middle class woman could fairly easily afford to be fashionable. Most women would have had a corset, stockings, a chemise, one or two petticoats, drawers, a nightgown, an everyday dress or a skirt and blouse (which was popular among women who worked), a Sunday dress, a coat of some kind, gloves and a hat at a minimum and maybe an evening/dinner dress. Women with a little more money would have had more of all of those things, and also might have had dresses that followed that prescriptive dress style that also existed in the Victorian era where there was a specific dress for the time of day or for anything you wanted to do. You want to go ride bikes? There's a dress for that. You want to serve tea to your neighbor in the afternoon? There's a dress for that. You want to sit at your dressing table and brush your hair before bed? Believe it or not, there was an outfit for that.

That is actually an incredibly complex and pretty much unanswerable question as much as asking how many items of clothing an ordinary woman in 2016 owns. It varies incredibly widely, more so on their interest in fashion or their job/life than their income sometimes! The biggest change that occurs around this time is that fashionable clothing is available to purchase of the rack or from a catalogue. In the late 19th century there was plenty of clothing available in that manner, but it was often the plainer styles that were meant for work or unfitted garments suited to lounging. The fit and structure of clothing in the 1910s changes in a way that no longer requires a fashionable shape to be custom fit to the body. A loose, blousing front means bust size can vary while the garment still fits the shoulders or waist. Mass-production of the same garment means it can be had cheaply, even if it is still detailed and stylish. A woman in the 1910s might not have more clothing than she would have had in the 1870s, but she likely has far more fashionable clothing. Unless, of course, she would have spent all of her money on that anyway! If you want to look into the subject more, I'd recommend looking into average income for the sort of woman you're thinking of (depends on country, etc) and looking up catalogue pictures with prices for clothing. Remember that she didn't have to buy cell-phones, computers, a car, or pay the bills on any of those things.