As Carl says, the power supply is not a problem. If you order it from
Amazon.co.uk, then it will have the correct UK style power plug.
There are some other problems depending on exactly how the OBi110 is connected to her landline and phone. Standard British Telecom plugs and sockets are different from US style telecom plugs and sockets. Various adapters are shown on the
Amazon.co.uk page to enable connections to be made.
Even if she is only using it to make and receive calls via her landline and the OBiTALK network, there are several changes needed to the configuration. For example emergency numbers need changing from 911 to 112|999 and the Line Port digitmap needs changing to suit UK number formats.
So it's not quite "out of the box", but there's plenty of UK advice available here on the forum.