God, people here can be real idiots...
Honestly, I'm not so sure there's a whole lot you can do for her, unfortunately. The problem with low self esteem is that she's going to TRY and pick out something wrong with herself, no matter what you say. I know how that feels, and I'm sure most everybody here does (admit it, we've all had times like that. maybe they didn't last as long, but every human being has felt that way at one point.)
Most of the suggestions given have been good ones, and I'd follow through with them and hope for the best, but chances are they're not going to help a
whole lot. Maybe she just wants the attention (because that's exactly how I get when I'm feeling attention-deprived...
) and if that's the case, she probably needs it. Spend a lot of time with her - make her feel accepted, like people want to be around her. I think that's probably about all you can do... :\
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Do you have stairs in your house?