Default already rooted i9300, just flash twrp to flash custom rom? Chinese phone

Hello, my cousin is already rooted.

This is a galaxy s3 from China, where she was. She says that either the play store worked in china, but not here, or never worked at all.

Fact remains, it doesn't work here. She's on tmobile, btw. and I think it's a chinese rom.

(i don't have the phone with me.)

When going to Recovery Mode, it looks like the stock recovery.

SO, in order to flash a new rom, in which the play store works, technically she could just download the .APK for Goomanager and then flash TWRP and then flash a custom ROM, something stable like CM10?

Also, apparently whenever trying to access settings, it crashes. So no clearing the app data for pLay Store.

ANy suggestions? THANKS!
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