I'm a lifelong bachelor, so you'll tell me I know nothing about daughters, but I have two nieces who grew up shooting with my brother (their dad) and me. The eldest got married to another gun guy and has my brother downstairs in the in-law suite (with a safe full of guns) and doesn't need any help from me on that score, but the littlest one asked me to buy one for her, even before she was legal to do so herself. I made a deal that day with her that if she would take her safety course, I would give her the gun she had requested for her 21st. I actually cheated a little and gave her the personal gun (same model, a Model 30) that I had bought from the estate of a recently deceased gunsmith buddy of mine, complete with Roy Fishpaw grips. The gun fits her perfectly and she can shoot a bad guy's eyes out with it, so when her husband the Marine can't be home, we all feel a lot safer. If she had asked for one of my other guns instead, it is quite likely she would have gotten it, and when I go, she and her sister and their cousin will likely get all of them, but this was the one she wanted and that was right for her.
I tell this long tale to bring out the point that your kids (even my nieces and nephews in this case) are what's important and should be your first consideration, with all your guns and other possessions just ethereal and passing through. I agree that the OP's #1 daughter should get the gun she grew up with NOW so he and she can BOTH enjoy it while he's still around. I'd also look for another well worn Model 15 for myself and maybe in his case, 2 more to provide each of the younger ones with a good sendoff when the time comes. JMHO, of course, and I'm getting to be a sentimental old fart!
Froggie