Took the GF shooting last night ... we've shot before, and she enjoyed it but wasn't super interested.  This was mostly AK/AR/shotguns out at the cabin.

Last night I took the Walther P22 for her, only took 2 boxes of ammo.  She burned through all 100 rounds and was looking for more, loved shooting the gun.

I'd like to buy her a semi auto .22

Something that will shoot well suppressed (rimfire can in jail).

Any recommendations?

I'm going to suggest the new Ruger Mark iv or maybe even the Mark iv 22/45 lite to come out early 2017.  The 22/45 lite will be threaded but the Mark iv's out now aren't.

Some reason you can't suppress the Walther that she loved shooting?

If you can still find one the beretta 71's that were being imported with the fake suppressor for around $250 are supposed to be real solid accurate reliable guns. I would much prefer an older metal ( steel or alloy) gun to the cheesey plastic frame stuff made today. The old
Smith 422 series is also excellent ( similar 250-300 price range) and the barrel is threaded and only need an adaptor for supresor use I am told. Also since the barrel is under the recoil spring on these adding the can does not obstruct the sights

Nope.  Already have the threaded barrel and plan to suppress it.

Just like the excuse to buy another gun!

I shoot a M&P 22 compact suppressed and it has been a fun and reliable gun. They all come with a threaded barrel.  I had a Ruger SR22 and it was a great pistol too. The Ruger didn't have a threaded barrel, so I didn't get to shoot it suppressed. It shot every kind of ammo I put in it and felt good in my hand though. My girlfriend loved the look and feel of the SR22 too. I'd recommend either one and will probably get a threaded SR22 someday.