Hi, Liz! I don't usually jump in like this, but I think it might help if I explained why she wouldn't fit in Slytherin. Hopefully it will help you to be more certain of the character you're trying to create.
See, the Slytherins are the mean ones, who play pranks and believe that they are better than everyone else. The personality section of your character says that she cares about everyone, and that her housemates made her a better person. That wouldn't actually happen, based on how Slytherins usually act.
Gryffindors are more about loyalty to their friends, helping others, and acting without thinking. All of those things are what you suggested Sophia would do.
That's where the problem comes in. She wouldn't make a strong Slytherin, and the hat probably wouldn't have put her there, even if her father might have been one. If you really want Slytherin, you'll have to make her more about thinking she is better than others, or make her harsher to those around her. Or, at the least, make her obsessively determined to get what she wants. Not all Slytherins are cruel, but she's simply too nice and too giving to be a Slytherin.
If you like her personality as it is, she really should be in Gryffindor.