Thieves aren't tanks, grunts, meat-sheilds or the like.

[TRP]

A thief regularly taking point has a wimp as a player.

[Clangador]

agreed. It's a great role for a Thief.

I CAN see the wife's desire to play a skilled/light fighter in AD&D that CAN contribute more meaningfully to combat. Perhaps suggest a Fighter/Thief next time she decides to make a Thief, or something like the Duelist from dragon magazine.

Alternatively if you use the UA, the barbarian can go this route pretty well (though the class as presented isn't good IMHO) & the Thief/Acrobat, justly maligned as it deserves, still has a GREAT melee equaliser in Tumble:Evasion %, hell an elven or dwarven fighter/thief-acrobat is a damnable opponent in a fight.

OR take a rule from 2e C&T where the Thief can spend a WP slot on being able to use a shield. Extra defense can go a long way, as magic shields are pretty common finds.

I use the Duelist as a PC class in my game.

[AxeMental]

Remember too DD, unlike the other PCs (with the exception of assassins) thieves are often (if not mostly) criminals (picking pockets, robbing, backstabbing etc.) they are taken along to the dungeon because no one else can do or wants that job. A criminal IRL may have alot of knowledge about how to break into homes, how to pick locks, how to hide effectively, but guess what. If they get electricuted...nobody is crying (not their victims not their bosses). Think about it, if they weren't expendable they'd be sitting in back with the group's cleric eating blackberry scones prepared by the groups halfing chef, rather then dodging spiderwebs and falling green slime up front.

PS, I'd say that hafling link boy is NOT expendable because he is demihuman and most likely good in alignment (which makes him trustworthy). His death would be more tragic compared to some slimeball NE thief (to anyone of normal alignment not totally overwhelmed with greed).

[Black Vulmea]

The thief should be focusing on enemy spellcasters in combat, sneaking in for the backstab whenever possible, or peppering with darts or throwing knives if not.

[genghisdon]

I use the Duelist as a PC class in my game.

Good on you, I do as well. The Bandit is also a good PC class. You might consider the OA Kensai as well.