IMO, GV is not a good value to Portugal. If you do want to use them, your mom will get better quality by not going through the OBi. Set up one of your GV accounts (or a new one) with her number. When she calls the GV number, it will go straight to the voicemail prompt, where she can press 2 to make an outgoing call, then dial the destination number, followed by #.
If you do want to route through the OBi, though you can record custom prompts (e.g. in Portugese) for the AA, you cannot change the behavior. With speed dials set up for her contacts, she could dial e.g. 22# for her sister, 23# for a friend, etc.
You can get much lower rates to PT with a SIP provider. That's easy to add when you get the OBi202; with your present OBi110 you would have to remove one of the GV accounts to "make room". Via a SIP DID, you could still receive calls on the second GV account. Providers you might consider are Callcentric ($0.0231/$0.0715 to PT landline/mobile, IMO top quality), Easyvoip ($0.005 / $0.06, IMO not the best) or Voxbeam ($0.0086 / $0.0493, good quality but entails some hassle).
Before installing an OBi in Portugal, confirm that you can get landline (or local VoIP) service with free or inexpensive calls to local mobiles -- in some European countries, such calls are more expensive than using a SIP provider.
If your contacts can make free or inexpensive calls to a Lisbon landline, they can call you via an iNum gateway (the call would be free to you).