No, definitely keep both Keep Alive and Mapping Enable to "Yes". It was just suggested that if it was kept at "No" it might explain your problem, but you have shown it is already correctly set to "yes".
IP's can change fairly frequently on ADSL connections, if the settings are not done right, so it is a possibility--if she is on DSL.
Changing "Answer Call without Registration" to YES would not materially help; there is no way to call someone by their Voxalot SIP URI (e.g.
number@us.voxalot.com) when the device is not registered.
You should put her device in her router's DMZ and see if that helps. Also, you could try shortening the registration interval to something less than an hour. I personally can't do anything knowing her account numbers, but maybe if I saw your saved Sipura configuration I could try to spot if anything is amiss.
--Chris