QUOTE
Why would she suddenly become flat on one note?
On the oboe, it's quite common!
For your daughter's birthday (or sooner) please buy a wonderful little book called 'A method for adjusting the Oboe and English Horn' by Carl J. Sawicki.
It probably has to be ordered from the USA, but isn't too expensive - especially considering the amount of money it saves you.
In the meantime, do the following:
Draw a quick sketch of the F, E and D keys on the lower joint and the adjustment screws.
Get a set of those tiny screwdrivers that cost almost nothing.
Very methodically, get your daughter to play D-Eb-E-F-F# over and over again, listening carefully to the E and paying attention to how the keys feel.
Turn the adjustment screw closest to the E key 45' clockwise. Mark this on your sketch - so you don't forget.
Repeat D-Eb-...etc Basically see if there's a difference.
Rotate it back, then further so it's 45' anticlockwise.
Repeat. Try 90' each way.
Try the adjustment screw next to it.
As long as you don't get confused over which screw you've turned, and by how much, you won't do any harm. In fact, it's impossible to do any real harm! A woodwind repairer will put it right in seconds.
N.B. Don't be tempted to turn them too much. Even less than 45' can make a huge difference!
All those small screws look terrifying at first, but in fact they're life savers. They allow the oboe to be adjusted far more easily than a clarinet.
Steve