6 is having issues wearing her pistol while out managing animals and needs a new belt.  She's been wearing a leather belt but the holster is sliding around and flopping because she doesn't want to tighten it down (she's only started carrying a few months ago).

Anyway, she's wearing overalls so no belt loops, holster has 1 3/4" loops, thinking a stiff belt with keepers is going to be the best bet.  Recommendations?

My girl uses a TheWilderness original instructor belt, same as me.  Ours are the softer 3-stitch, but they offer 5-stitch and polymer lined as well, for increased rigidity.  They are offered in 1-1/2" and 1-3/4" sizes.  Check them out.  They also offer lifetime warranty on the velcro...just send them back for new velcro.  Pretty sweet.  The one I bought in 1999 is about due now.

http://www.thewilderness.com/belts/

How are keepers going to work with no underbelt and no belt loops? I'd suggest a belt lined with velcro then an HSGI micro grip belt liner to keep it from shifting. A propperly sized and adequately thick nylon belt will not let the holster shift. A 1.5" thick belt that has enough layers to be thick and stiff should be fine. I believe male velcro on the belt makes the most sense,  and an Austri Alpin buckle for convenience. A plastic Austri Alpin 2nd choice. A standard plastic buckle 3rd and an old school riggers belt method of attachment like wilderness last. She wont want to wear it unless it is convenient.

If the holster flops out at the bottom it is usually too low. People like to drop offset their holsters too much IMO. The top of your handgun should not be below the belt line or it will flop no matter how stiff the belt.