The one that Wally brings home for dinner and she says she is going to night school.

Does she play in My Three Sons, the one where Mike takes the girl from the "wrong side of the tracks" to the dance and nobody wants her to go?

The late Diane Sayer (Marlene, season 6) on LItB did not have a My Three Sons credit.

She was a good actress always seemed to play the wrong type of girl.

She definitely nailed this role. I'm sure it was a memorable episode for Tony Dow.

I also thought that Diane Sayer was the same girl who was in My 3 Sons. I thought she was the one who worked in her father's diner behind the counter and Mike was going to take her out. But I just did a bit of research and found out the girl who did play that girl "from the wrong side of the tracks" on My 3 Sons was Penney Parker. She looks alarmingly like Diane Sayer, fortunately Penney is still alive. Here's Penney Parker, no wonder we all were thinking she was Diane Sayer.
https://secondhandsongs.com/picture/127426

Here's Penny sort of colorized:
https://www.sitcomsonline.com/boards/attachment.php?attachmentid=272844&stc=1&d=1645652275

Here's Penney's "twin", Diane Sayer, all cleaned and scrubbed:
https://www.sitcomsonline.com/boards/attachment.php?attachmentid=272845&stc=1&d=1645652593

Here's Penney's "twin", Diane Sayer, all cleaned and scrubbed:
https://www.sitcomsonline.com/boards/attachment.php?attachmentid=272845&stc=1&d=1645652593

Very similar and they sort of played similar roles bein girls not from "the regular group".

I also thought that Diane Sayer was the same girl who was in My 3 Sons. I thought she was the one who worked in her father's diner behind the counter and Mike was going to take her out. But I just did a bit of research and found out the girl who did play that girl "from the wrong side of the tracks" on My 3 Sons was Penney Parker. She looks alarmingly like Diane Sayer, fortunately Penney is still alive.


Off topic: Penney Parker also played the replacement Terry in a marriage story arc for season 7 of The Danny Thomas Show. Her husband-to-be was played by Pat Harrington Jr., who had a future main-cast role in One Day at a Time. The original Terry on Make Room for Daddy/Danny Thomas seasons 1 thru 5 (and I think a few episodes of season 6 before she left) was Sherry Jackson.