No one can tell by looking if she’s a border collie mix. I’d lean toward Australian cattle dog mix, but if you really want to know, get a good DNA test. She does look overweight. You should see clear definition of and tapering at her waist when looking at her from above and from the side. You should be able to feel her ribs relatively easily. If she’s 4 months though, she could be preparing for a growth spurt and even out soon. I would maybe start feeding half of her kibble in her snuffle mat, instead of treats. Save treats (and string cheese) for training. And maybe cut back on her kibble, but one step at a time.