You could ask: How do we KNOW that all religions are the same??
This demands just as much 'proof' and 'evidence' as the position that
'All religions are NOT the same'.
However, a slight problem with simply stating the above to your friend
may be that it could be deemed as overly 'confrontational' and there's
the temptation of getting comfy with merely proving the person wrong.
Many times over the e-mail (when posed 'anti-Christian' questions by die-hard skeptics) I've given systematic or 'intellectual' answers but somehow I doubt that this is what sincerely-seeking people need or are even looking for. Evangelism is VERY different from apologetics, yet I suppose the 'academic'-type answer can still be given, but only as a interdependent 'bridge' to more personal sharing.
On the one hand we need to understand the issues surrounding absolute
truth, religion, etc. yet we must be careful not to let such (possibly)
'high-brow' thinking cloud out the personal aspect involved in sharing
Christ to someone. I feel it's a life-long discipline to integrate
both sensitive love and strong thinking into our interactions with lost
yet searching souls.
As members of Christ's body, the evangelist cannot say he doesn't need
the apologist, nor vice-versa (especially in our society which places a
merit on good strong reasoning).
So back to the question...
I guess a more sensitive approach would be to ask her what she considers
to be the same. Is it because they all teach people to do 'good'?
(This is usually the answer).
In that case, you could share that the Christian motive behind doing
good - Because God died and gave Himself for us, and so we are to reflect
His Spirit in our lives by showing His fruit; because God Himself is good
(God is love!) and so we as his children 'naturally' should love one another,
etc., etc.
You may also want to mention that 'good works' in the Christian faith is NOT a 'means' to salvation but simply a REFLECTION of saving faith in God. So it's : "I do good BECAUSE I am a child of God" and not, "I do good IN ORDER to be saved".
The above is rather distinct from the Buddhist, Hindu and Islamic 'reasons' for doing good, both of which are a means to salvation. A Buddhist does good in order to break himself from the wheel of life and achieve Nirvana, etc.
So, even relating to the question of 'good works', there are major differences between our beliefs and that of followers of other religions...
A gradual follow-up towards 'diffusing' the question could be our sharing of Christian theology (this is normally mentioned briefly in evangelistic tracts but let's always be prepared for more in-depth questioning):
Then it's your cue to point (and lead) her to the Only Way, Truth
and Life. *smile*
Regards,
AL