The LUBA Mini's ability to handle your mother's lawn situation depends on several factors. Regarding the 1cm gravel path steps, this depends on the gravel thickness and how soft the terrain is. While the mower can handle small obstacles, these steps might be an issue, and creating a small ramp at these transition points would be beneficial for smooth operation. For the lawn adjacent to the river, you would need to create a wider boundary zone in the mapping to ensure the mower maintains a safe distance from the water's edge. This extra buffer is essential for safety, especially considering the potential consequences of the mower entering the river.

Given your mother's large lawn area (1200 sq m across 6 zones), you would be better off with the full-size LUBA 2 AWD rather than the Mini. This larger model will reduce mowing time significantly and require fewer battery cycles, making it more efficient for the property size. Regarding connectivity, the mower will continue to operate without 4G/Wi-Fi - you'll just lose remote control capabilities. Loss of GPS signal is not a critical issue as the mower will automatically switch to using its camera navigation system. The RTK base station has a good range, but proper placement is key for optimal coverage across the 1.5-acre property.

If you could extend the Wi-Fi then iNavi could be used and there would be no need for the RTK station. For more information on the iNavi and the full size mower, see my links below -

https://easylawnmowing.co.uk/luba-2-awd-review/
https://easylawnmowing.co.uk/inavi-service-explained/

Hope this helps
Mark