Declawing is cruelty, plain and simple. It's removing most of the toe, and causes severe pain and discomfort. I have seen cats become utterly miserable from it and turn into complete imps.
It can cause severe behavioral problems because the cat is now defenseless and in pain. Often times cats will stop using the litter boxes because of discomfort and just go in the floor, they become antsy, angsty, aggravated, and just overall mean.
And it confines the cat to being indoor for life. And if the cat ends up miserable and not only a strictly indoor cat but also being declawed...
Scratching comes with cats, like barking comes with dogs. You can use training to teach a dog to be a little more quiet, and you can provide a cat with exercise and toys/objects to decrease scratching.
Some cats are perfectly happy being strictly indoors, but most are not, and I can't imagine a barn cat being happy inside. I honestly believe cats are much happier if they have the option to go in and out as they please.
I have a strictly indoor cats, Draevyn, and an indoor/outdoor cat, Killian. I can tell you that Killian is 100% calmer, more pleasant and far more obedient then Draevyn. He's also in better physical shape.
I would just leave her. Have her spayed, let her recover, then turn her back out. She'll get to live her life as it may be and she won't be put through the stress of having litter after litter.