You don't need a magnifying glass to see ticks. They are fat and brown and can range in size from extremely tiny(pin head size) to as big as the tip of your thumb. There looks to be one on her cheek/in front of her eye in the picture, but maybe it has already drank its fill and fallen off. You may want to go ahead and treat everything anyway with the Provent-A-Mite just to be on the safe side, as you may wake up one morning and everyone(the snakes) is crawling with ticks.

Where is the boa quarantined? And where is the new Ball quarantined? You need to be EXTREMELY diligent about using all separate equipment when dealing with these snakes so as not to pass anything to your other two. Deal with your original two Ball Pythons first, wash your hands and arms, and then go deal with the two in quarantine. Ball Python first, and boa last. After you are done with the boa, change your clothes and wash up very well with warm, soapy water. Or even go as far as taking a shower.