It is more than likely the hell-on-earth that is female puberty.
Your own experience may make you extra sensitive to the apparent sings of your condition in others, which may or may not be well founded.
You should have a chat with your daughter, when you are both alone, and have some time. Ensure that there is nothing bothering her, and make sure that she knows that you are avalilable to talk to, with no judgements or rows, if she needs to 'unburden'.
She may not feel that you are the appropriate person in whom to confide - and that is not a problem - the problem is if she has no-0ne to turn to, that is when simple issues become complex in teenage minds.
Make sure you affirm her as a valuable person to you, and to the wider world, on a daily basis - just a simple "You're doing fine, and I love you ..." is all that's needed during this time when self-loathing is a daily occrence, together with peer pressure and shifting dynamics in friendships.
Keep an eye on her generally, and if you think she is actually slipping into depression, have a word with her Head Of Year at school. who may be able to offer additional support from that end as well.