Hi there Ken
This is a common problem where the reed supplied with the new instrument is probably a fairly cheap and cheerful affair, badly scraped, probably not wired or, if so, done incorrectly and the whole thing is a bit of a disaster. At least, this has often been my experience with new oboists turning up for their first lesson with an instrument I haven't selected for them (Mum and Dad just went out and got something, despite my request not to

)and with a reed "supplied by the shop".
Others have given you good basic information about the embouchure shape and soaking the reed properly (only the cane - not the whole thing!). However this, alone, may not sort it. If it is too wide open, you will need either to get it wired by someone who knows what they are doing or at least apply pressure on the top and bottom of the cane (not at the sides) with your fingers - gently so you don't split it - until it closes a bit. However, if the scrape is wrong, no amount of soaking etc will sort it to be ideal.
For a new oboist I would always use a medium soft reed or possibly a soft reed for a week or two, increasing the strength as they gain in confidence. Oboe playing is also, of course, a very different thing to flute or saxophone in terms of embouchure (and hugely different to brass) so don't expect just because your pupil is already a woodwind player that they will just pick the oboe up and play it immediately. Please make sure that they don't try to play the oboe with a saxophonist's embouchure either - I have lost count of the hours I have spent in my teaching career modifying/sorting out embouchures etc from people who've come to the oboe after playing sax or clarinet and still try to play the oboe the same way. That's why I never teach another orchestral woodwind instrument, although I can play them, because I still believe each instrument needs to be taught by a true specialist if at all possible (not always the case with music service provision of course and no offence intended to all our hard-working peri colleagues on these forums).
I cannot stress strongly enough the value of getting your student a few lessons from a specialist oboist if at all possible. They will set them off playing correctly and check out the reed issues, dealing with them appropriately. The oboe (and especially reeds) can be hard-going initially but the beauty of the instrument will win through eventually.

The fact that your pupil is already a woodwind player will help of course, though (as mentioned above) please treat each of his/her studies as very different instruments to play.
Hope this helps. Please feel free to PM me if you have further questions.