Yes it appears she is holding. I remove the female from the tank if it is stocked for pure fry (four or more females for every male and no species that crossbreed with yellow labs) after 18 days of holding and if I want to raise/sell 20 yellow labs.
The terrapin risk is that the reptile will eat the mom all the time...not just when she is holding. And the nitrates in the tank. Everyone will eat the fry once they are spit, including the parents.