There are snail&bug baits (not a powder or pellet but more like sawdust) that kill/control ants that can be mixed into the potting soil. I wouldn't use it on any edibles, but for flowers, the ants leave.

Raise the pots off the ground by using pot feet, or bits of roof slate, anything that lifts them up slightly, leaving the main part of the bottom of the pot off the ground - dust the surface underneath with ant powder regularly, particularly after rain when it will have washed away. As for the pots themselves, if they're infested with ants already, turn out the compost, clean the inside of the pot, dust lightly with ant powder. Use half a jeycloth (or weed membrane, if she has any) and place it at the bottom, over the entry hole and partially up the sides of the pot, not to block the drainage (both materials let water through) but to block ingress by insects to a degree. Now fill with fresh compost, plant up, etc., and stand the pot on its feet or whatever you're using.

Sounds good to me. Thanks for your response.
macpat.

Thanks for your suggestion. I will look for this ant bait. Do you by chance know a brand name?

Nippon used to make ant powder, hopefully they still do - I know they still make ant bait in the form of sticky liquid. Powder comes in a plastic bottle shaped puffer pack, usually about 9 inches high.

Many thanks!