The visitors needed to win all three of their remaining ODIs in order to reclaim the series. Instead, England failed to recover from the loss of early wickets and ultimately fell short of their 206 target.
Australia have held the Ashes since 2014 and that will continue to be the case with the team currently leading the series 8-4.
England captain Heather Knight said: "Our mentality in this series has been really good. We haven't been able to quite get over the line, which is a shame, but we believe we're good enough to beat them and we've gone toe-to-toe with them in a lot of aspects, but we just haven't quite been able to have that killer instinct and get over the line.
"I guess maybe when you let a couple of things slip, they are the sort of team that are going to make you pay for it and not give you a second chance.
"I'm not worried, I think the belief and the mentality has been great this series, unfortunately it just hasn't come off."
England can still draw the series should they win their remaining two ODIs. Knight, however, doesn't see that as much of a consolation.
She added: "You come out here and obviously the goal is to try and get the Ashes back and there's bound to be a bit of disappointment.
"I thought we bowled outstandingly and were actually really unlucky. We bowled perfectly to the plan, we adapted to the pitch, then just kept losing wickets in that chase. You would back yourself to chase that.
"I thought the Aussies bowled very well, but we just couldn't string that partnership together and kept losing wickets and I guess in the three games that we played we haven't been able to string batting and bowling together and put in that complete performance.
"But I'm proud of the way the girls have fought. The lower order I think kept us in it a little bit and kept the hope alive, but unfortunately the Ashes have gone."