My wife rides with platforms and I've gently suggested clipless pedals, but haven't pushed her at all - the reason, even the first or occasional fall (we've all done it) could really set her back both mentally and physically. Plus, even though I really do enjoy clipless pedals and use them 99.999% of the time, I also don't believe they add a meaningful amount to a slow, recreational rider's speed or power. To me, they do make the ride more enjoyable.
All that is leading up to: I put some of the knobby/grippy BMX type pedals on her mountain bike and she really likes them. They do hold the foot over the occasional bump very well.
Lots of options and price points.
Also, power grips work very well on conventional flat pedals:
On our tandem, she uses clipless - Speedplay Frogs - because her foot was tending to bounce off the pedal going over bumps or when the shift was hard. On a tandem, it can be very dicey to get the foot back on the pedal without barking your shin. Plus, on the tandem, the way we ride it, she doesn't unclip until we're actually at the end of the ride - I unclip and hold the bike when we stop, she provides the power to get started.
The Speedplay Frogs are the simplest clipless pedals I've ever seen (I did use them for a while myself too). She had a lot of difficulty getting into the SPD's, and has no problem with the Frogs. The easiest to clip into for the inexperienced, the easiest to clip out of (no clipping actually - just a simple rotation out). If you're having difficulty with SPD and want to use clipless, try them.