she using a old phone, samsung a6, I also tried on another old phone xiaomi redmi 5a
tried simba voice app but seem like only works when calling out, unable to receive call.
Samsung A6 is quite an old phone. I suggest getting a new phone. Since it's Samsung, get her a similar Samsung phone, like A15, A35 or A55.
Why new phone? Cos old phone does not support new security updates, very risky for old age parents, risk of virus and malware or scam.
If simba voice app does not work when receiving call, you might want to go to your phone settings, under default app settings, for call app, make simba voice app your default app for calling.