Tankmates for a cinnamon clown

Hi
I have a 55g that's almost ready to accept my adopted cinnamon clown. It's got 55+ lbs of base rock and a bit of live rock, a bunch of caves, and a lot of swimming room. The structures/piles of rock are mostly on the back of the aquarium, but they can still be traversed in/through. So the questions have to do with stocking (besides the clown).
Said clown came from a tank with a bunch of other damsels, and she had to defend her territory (a rock arch) a lot, but now that she's alone, if I feed her brine shrimp with a pipette she cautiously approaches the pipette. So she can be very territorial (though she's never hurt anyone, and yes, she had been previously paired), but she can also be timid.
I was wondering if putting a valentini puffer in there with her (after a quarantine period, of course) would be a safe thing for both of them. I don't plan on a reef any time soon as I have zero time for that right now with school and all, so that shouldn't be a problem.
Also/if that wouldn't work, would a gramma basslet be acceptable?
If both don't seem like good candidates, maybe you can suggest something to me that won't cause anyone involved pain and/or suffering due to territorial disputes.
Thanks in advance!