See what inspires her, and what interests she has... she can join the clubs at school which interests her... thereby, she will be amongst other kids that have the same interest.
Or, in extra-curricular activities...
If she engages in things she likes, this can boost her self-esteem...
it seems MAYBE she is hiding beneath baggy clothing, because she feels insecure about herself... but, a child should not be forced to dress differently and learn how to be comfortable in their own skin.
There is a girl in my daughter's class, that dresses like that... she is not girly, nor likes girly things. As she gets older, it may impact her in social ways as well... which does happen sometimes. BUT, this girl is confident...and her parents let her participate in things she likes, like golfing and tae-kwan do. And her parents let her dress as she likes, as long as it is not grungy. And they always are proud of her.... and encourage her own self-identity and "style" even if she is "different."
Mostly, just keep close to her, and build up a good solid communication habit....whereby she can come to you as a soft place to fall and a place where she can express herself unfettered. She is hitting the pre-teens, and her comfort level with you/Dad will be paramount in how she navigates through it....of course, your wanting her to engage in good friends and activities. Not seeking out negative social outlets and bad habits or hiding things from her parents.
And YES, her relationship with her Dad will also color her world and how she feels about herself. Little girls "need" Dad as much as their Mom. They will need to know how to engage with "boys" and to NOT just seek approval in negative ways with the "wrong" types of guys/friends.
....try asking her Teacher perhaps, if there is a social problem she notices in class or at school, regarding your daughter. See what the Teacher suggests....
And of course, nurture any "talents" or interests she has... maybe if she feels valued and recognized for her talents, she may blossom.
Not all kids are good with the "shrug it off" approach to handling problems. So, see what approach will help her. Teach her about how to discern between feelings and how to cope... coping skills can really give a child more confidence and a sense of "control" over their day to day problems and feelings.
All the best,
Susan