It’s harder to reply to this due to the prohibition on commercial links, but I’ll try. I’ve been carrying concealed for decades, even in non-permissive environments, and my wife is a retired fed.
This is an option from Urban Carry, who is a sponsor: https://urbancarryholsters.com/g3-mag-holster.html
I’ve never used the UC G3 mag pouch, but I can see how it would be a good solution in some circumstances.
Galco, another sponsor, has a number of similar OWB carriers they market as concealable, but I don’t own any of these, either: https://www.galcogunleather.com/ammunition-carriers_8_450.html
I own and have owned a BUNCH of concealed mag pouches for various hand guns from pocket pistols to full size 1911A1s, with several poly-pistol stops in between. I’ve had to dress in everything from jogging shorts and a t-shirt to jacket and tie with slacks over the years; this would include quite a bit of coveralls and other blue collar work apparel. Pretty much the full gamut. I’m thinking about biz casual options for women.
My favorite for single mag pouch for IWB versatility is the Creatrill IWB Tactical Mag Holder with magnets in them. For a micro or sub-compact single stack, these are good…and proven. We carry them frequently with single stack M&P mags in a sub-tropical climate. They are invisible and reliable as a “deep cover” mag pouch. You can use these several different ways.
The Sticky Holster Belt Sliders are another handy gadget, but the retention is not terrific. I believe they are another sponsor here. Not sure. So I won’t include a link. Their Mini Mag Sleeve and Mag Sleeve deserve a look, too.
My favorite (if she wears pants) is the DeSantis Double Ankle Magazine Pouch. I’ve used these extensively. Good value! Worthless in a skirt/dress.
A very handy gadget for her kind of stuff if she wears a belt with a cover garment is the Safariland 123 Concealment Magazine Holder.
Finally, have here take a look at Stashbandz on Amazon. They have a variety of covert pouches on thigh garters and waistbands made specifically for women who want to hide small objects on their body. I’ve never used these, nor has my wife. But I know a few women who swear by them for skirt/dress concealed carry of mags, knives, small flashlights, tiny IFAKs, etc.