I am assuming from your question that this attack didn't just happen yesterday? If your Min Pin survived the attack with just the 4 solid "bumps" on her abdomen, she was truly quite fortunate!
When the skin is punctured by another dog's teeth, there can be soft tissue swelling and/or bleeding into the area. This swelling and the accumulated blood can then result in firm lumps of scar tissue. If your Min Pin was lucky enough that the teeth did not penetrate into the abdominal cavity, then those bumps might be the only remnant she'll have of the attack. If she is moving around easily, eating and drinking normally, urinating and passing stools with no changes in pattern, and is not painful anywhere on her abdomen, then she will most likely be OK. However, if you notice any different along those lines, she should be examined quickly.
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