My friend won't talk to me? help!?!?

ok so my friend (Sara) and i have been friends since the start of the school year in spanish. So we would talk to eachother and say hi and stuff but never really hung out. Then she broke up with her bf and one of her best friends who she always hung out with said they were glad Sara broke up with her bf ( Bob). then they stopped being friends. I felt bad for Sara, so i said you can always hang out with me whenever you want. She started hanging out with my friends and i and she felt akward and would always say she wants to walk around after like 5 min of sitting. Of course my friends and i did not want to but we did. Then one of her friends (Kyle) started hanging out with us.We have all been hanging out for about a month now just walking around. Yesterday, Sara seemed annoyed because kyle sent her a text saying " I don't know how to say this but when you and your ex were together, my girlfriend slept with your boyfriend, i broke up with her because of it, but i never told you that because you were going through so much drama at the time" Sara replied "No! he would never do that to me! he is not like that" she got really mad. Apparantly Kyle's ex hated sara. Sara then showed me the texts from Kyle and her other friend Matt. They both said the same thing. After seeing the texts I said "I believe it." BIG mistake. She said wow i cannot believe you, and stormed off to the bathroom. of course i went after her to see if she was alright. She slammed the stall shut and started crying. There was no convo for 10 min. She came out, I said " Are you ok? I am sorry for what i said, i was just giving my opinon and not thinking" I went to give her a hug and she bumped into me and stormed out. She went up to a group of her 'friends' and gave a girl a hug. The friend said "aw sara, its ok!" Then Sara said to her friend "come with me to my teachers classroom!" and sped off. I just left and went back to my real friends. I HATE drama! Then after lunch i saw her in class, she did not speak to me at all even when i tried to apologize and talk to her. So now she is ignoring me and i don't know what i should do. Also her birthday is on Friday and i said i would get her something like her favorite food or drink... but now i don't know if that is gonna happen. Pleasse help! BTW sorry for making this long but i felt like detail was needed.

Oh and she sits right next to me in class sooooo what should i do???!?!!?!?