If you want an ally to do a little bit of attacking or thwarting and then block the villain, most other Protection allies are better than Protector at the attacking/thwarting or cheaper to deploy. If you want an ally to repeatedly block minions Victor Mancha is much cheaper, though you could consider Protector a redundant option until you can find Victor.
She can be a decent home for any spare Tough status cards you get from Hex Bolt, "We Are Groot", Muster Courage, or the like - it gives you the option to convert the Tough card into 3 damage, if you'd prefer that to absorbing a Villain attack.
One situation where Protector is great is repeatedly paying to Thwart. Protection has a tough time actually clearing threat, so being able to repeatedly spend one resource for one threat removed is a good value.
The other situation is when you just want to convert resources to damage, another area where Protection doesn't have many options. Paying 4+card for Protector to attack twice for a total of 6 damage is not great compared to what you get in Aggression, but it's not bad for Protection. And you have the option to spend 4++card to attack three times for 9 damage, or 4++card for two attacks and a block.
Overall, I'd say Protector is best in a deck that can reliably generate to help keep threat under control, with the ability to throw out some burst damage at key moments.