On the contrary.. haven't you heard the news?
Nokia is about to release brand new symbian running phones and the fate of Symbian is not yet concluded.. until the real Fat lady sings...
Nokia announces Symbian smartphone event for April 12 -- Engadget
Nokia schedules a Symbian event for 12 April, gets even with HTC - GSMArena.com news
I doubt Nokia will discontinue symbian as most of the mass market/consumers like China and India are still patronizing their Symbian Nokia products.... Win 7 OS is still in its infancy... there are still to many ups and turns getting that OS...
on Androids side... well.. the word portability and customization are there.. BUT.. it is more patronize to people who have the keen side to tinker and explore their android phones true capabilities...
if the sister of your GF is not into the tinkering or upgrading an Android OS phone.. and her usual needs is just texting, internet and making calls... then I would suggest, you recommend her a Symbian Nokia phone still... Userwise and application-wise.. there are millions and millions of symbian apps already out there in the web.. just ask Mr. Google for the right apps.. and presto it can be downloaded on to your phone..
The Android market is growing.. but most of the applications are still in their infancy.. though the potentials are there... but then again.. nothing beats a symbian app that has been tried and tested to work over the years already.....