How long can I leave my girl alone?

Since both my parents died I'm now alone with out family dog. Now after everything has settled a but I need to work to be able to pay my bills. She is 10 years old and almost the whole time my mum or dad were home. I work 6h a day and need around 15min to get there, so she will be alone for 6,5h a day. For the first week I always got someone to check up on here during this time but thats not possible for ever. Is it ok to leave her for 6,5h or should I talk to my new manager and try to get to work 5h a day (less won't make enough money). I walk here before and feed her. I just don't want to neglect my baby because the last wish of my mum was that I take good care of our dog. Maybe someone has a good idea what else could work or if the 6,5h a day are ok for her.