If I came back for this cat, would her behavior change?

About a month ago I found a stray cat and kept her for 2 weeks. I would have adopted her but she was very aggressive towards my other 2 cats (1 male, 1 female, are de-clawed, female cat is very old and has no teeth) and scratched and bit them and hissed at them. So I wanted to keep her but my mom took her to a non-euthanizing animal shelter and she is still there. I miss her very, very much and I'm kind of depressed. I regret more than anything taking her to the shelter and I want her back but I can't because I want my other 2 cats to be safe as well! Last night I was talking with my sisters and we thought that maybe she would realize why we took her there and be nice to our cats. Would de-clawing her help keep my cats safe? Also, if we got her spayed would that change her behavior? I'll do anything to get her back! I don't know what to do without her!