Get the terrier spayed ASAP. This should greatly minimize these attacks. The terrier is a mature adult now and is acting like one. Same sexes in dogs won't always get along, especially when one is fixed and the other isn't. The terrier is hormonal and territorial. By giving the terrier more of your attention you're spoiling her and she doesn't want to share you with the lab mix. These attacks seem to be happening when you are around, so you are what the fights are all about.