lol what a silly attempt. She is assuming heaven exists and from there is saying that his going there by horse back is scientifically impossible. However, thats rather foolish because if she is already assuming that heaven exists then she is implying that God has the capacity to create heaven, but is not able to allow Prophet Muhammad pbuh to travel there by horse back!

He didnt go by horse in the first place, it was a special animal called a 'buraq'.

Honestly, what dont people understand about miracles? You just cant use science to prove them wrong, thats why they are miracles!

Well maybe if you just said, "I personally do not have all the answers as am sure you will appriciate, so please, I invite you to a forum which I trust and I go to, to understand and learn abit more about Islam, I am sure you will be able to debate there", give her this site, then tell her, "my debating skills are not tremendous nor am I infallible, so if you truly would like answers please visit the site and ask there as more knowledgeable people than me will provide you with better answers. Peace."

Thats it sis