I'm going to hit two questions with one stone here. Yes women should always dress modestly. There are a lot of guys that keep on sining becuase of the way girls dressed and if they dressed differently most christian guys would sin sexually a lot less. Some of that is the guys falt also.
Since I'm 16 I don't have either, but when I do get a wife as long as she wears modest clothing in public and at parties I'd be fine. At home I wouldn't care what she wore, until we have kids. If I have a daughter If I find her wearing something I didn't approve of I would make her change then go and throw the clothes in the trash.
Yes girls can dress modeslty in pants. I actually think a lot of girls actually look better in baggier pants then tight pants.