Pull the dipstick and check the condition. There would be an external filter. I’d be more concerned about the timing belt if there’s no service history. If it was changed when she bought it. It may be time for another change. The six speed is extremely easy to do. Measure what comes out cold. Add that amount back in. Start her up till the fan kicks on. Shut it off and check the level. I use Amsoil SS blue cap ATF in my wife’s 19.