I don't mean to upset you or insult you by saying this but Banfield is widely known for wanting to do unnecessary procedures, give unnecessary vaccinations, etc. in order to increase their profit (I'm not saying that all of them are this way, but many of them are). It doesn't surprise me that they're urging you into two separate procedures where you'll have to pay twice. Especially if you bought into their "insurance" plan and prepaid for the spay.
My vets have always strongly encouraged me to have the baby teeth extracted at the time of spay/neuter. There is always a risk any time anesthesia is used on people or pets. My advice is for you to check with a different vet.
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He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devotion. -- Author Unknown