If I was spending my money, I'd spend the extra on the Single Six, over the Wrangler. It just seems to be a little better made, with somewhat better materials - if you can believe the reviews. Ruger makes it for half the cost of a Single Six - that's bound to show up in the gun. The Single Six's trigger is a pound or two lighter. That being said, I'm sure she'd be perfectly happy with the Wrangler - you'd have to shoot them side by side, to notice any difference - and that would be slight. I really like the all steel construction of the Bearcat - it's a sweet little gun - but Man ! - is it ever tiny. If Ruger made an all steel Single Six, I'd definitely have to buy another one.
I'm surprised you can't find a 5.5" model - that's what both of mine are. Don't think I've seen a 6.5" one.
Good luck with your decision - and just to add some more angst to your choice, there's a saying, that - No one ever regretted paying for quality.